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Computer starts to boot, then shuts off. Successfully boots after 3-4 tries


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#1 kjm782

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Posted 14 November 2010 - 06:07 PM

Hello,
I am having problems booting up my computer. This is only an issue if the computer was previously off for a few hours. (If I am just restarting there is no issue.) Usually the computer will start to boot up (lights and fans come on and I see the POST screen come up) and then after a few seconds it just shuts off. If I do this 3-4 times the computer usually starts up and everything is fine.

I've also tried going right into the BIOS when the computer starts and if I do this it will usually stay on while in the BIOS menu. (If I exit the BIOS right away, the computer will shut off a few seconds into the POST process.) I'll let it sit for a while in the BIOS menu thinking that maybe if it has a chance to warm up it will be ok. It is tough to tell if this really makes a difference though.

The computer is about 2 years old and I haven't really made any hardware changes in the last year. In fact, it has probably been a year since I last opened the case. I opened it tonight to see if there was excessive dust that may be interfering with the fans and that doesn't appear to be the problem.

I am assuming that this has to be a motherboard or a power supply issue? Unfortunately I don't have any spare parts to swap out to see which is the culprit. I have a 520w power supply and my motherboard is a Gigabyte GA-M57SLI-S4 (rev 2.0).

Does anyone have any ideas for what I could try? Thank you in advance for your help.

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#2 dc3

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Posted 15 November 2010 - 10:27 AM

If you have a multimeter which reads DC voltages you can check out the PSU for proper rail voltages. The tutorial which I'm posting below can be used for this test. In your case it would be beneficial to set this up and then start your computer while it's cold to see what the +12V and +5V rails are reading before it shuts down. Read these one at a time until the computer shuts down and record the different voltages.

Another test you can do is to start your computer from a bootable disk. You may need to change the boot order in the BIOS so that the CD-ROM is the first device in the boot order. If it fails to boot from the disk this will indicate a hardware failure.

Reading PSU Rail Voltages

Caution: Please read this before continuing.


∑ Since it will be necessary for your computer to be on during this procedure, you need to be aware that you will be working with live 12Volt DC potentials, which if handled improperly may lead to electrical shock.

∑ There are electronics inside the case that are very susceptible to electrostatic discharges. To protect your computer, touch the metal of the case to discharge yourself of any electrostatic charges before touching any of the components inside.

∑ If you are not comfortable doing this procedure, then I would suggest that you not use this tutorial. The risks involved are minimal, but are there nevertheless. Anyone who uses this tutorial will be doing so at their own risk.


There are two devices commonly used to read the rail voltages: a PSU tester, and a multimeter.

The PSU tester is the easiest to use since all that is necessary is to plug the different connectors into the tester and read the results on the LCD display. The problem with most of these is that they only perform a pass/fail test. They will not provide you with actual voltage readings.

There are a variety of multiple meters, but this tutorial will address Analog and Digital multimeters. The advantage of these meters is that you will be able to obtain accurate real time voltage readings.

For those of you who wish to know more about multimeters there is an excellent article in Wikipedia.


Analog Multimeter

Posted Image


An Analog multimeter is a little more complicated to use. Both Analog and Digital multimeters need to be set to the appropriate voltage, but with an Analog multimeter, you will need to choose the voltage range and must read the proper scale.

The Analog multimeter uses a needle display which moves from 0 across the scale until it reaches the voltage being tested. This multimeter has five major linear divisions with multiple scales to read a variety of ranges. An example would be three different ranges. The first is graduated in increments of 0 through 5, the second, 0 through 10, and the third, 0 through 25. Each of these ranges are subdivided into divisions that are graduated into tenths. In order to read 12 volts the 0 through 25 range would be the appropriate one.

Because DC voltage has positive and negative potentials this device is polar sensitive, this means that if you reverse the two probes when reading a positive DC voltage it will read as a negative voltage. This is actually necessary to read negative DC voltages. The two probes are differentiated by their color, Black (negative), and Red (positive). To read a positive DC voltage, the correct probes must be used with their corresponding potentials (positive to positive and negative to negative).

With the probes being used normally to read a negative DC voltage, the needle moves from the 0 to the left, "pegging" the needle. By reversing the probes you can properly read the negative voltages.

Digital Multimeter

Posted Image


The Digital multimeter (DMM) is much simpler to use. As was mentioned previously, you will need to set the appropriate voltage. One of the advantages is that the DMM has an LCD display with a numeric readout, so there are not any multiple scales to read. Another advantage is that most DMMs are autoranging when reading voltages, which means that you will not need to set the range with these DMMs. A DMM will read both positive and negative DC voltages and display them correctly. When reading a negative voltage, a minus sign will appear on the display before the numeric value. This still is a polar sensitive device, so you will still need to use the positive and negative probes with their corresponding potentials.

There are five different DC rail voltages which are color coded. The Black wires are always negative.

Yellow +12VDC

Blue -12VDC

Red +5VDC

White -5VDC

Orange +3.3VDC


There are only three voltages that can be measured easily without disconnecting the 20/24 pin connector from the motherboard: +12V, +5V, and +3.3V.

The +12V and +5V voltages can be read from a four pin Molex power connector.

Four pin Molex power connector

Posted Image


The same voltages can be taken from a four pin SATA power connector, but in order to read the +3.3V you will need to read this from a five pin SATA power connector as seen below.

Five pin SATA power connector.

Posted Image

To read these voltages you will need to insert the Black (-) probe into any of the black sockets, and insert the Red (+) probe in the different colored voltage sockets. To read the voltages from a SATA power connector it is easiest to insert the probes into the back of the connector where the wires enter. Unfortunately the sockets of the modular SATA power connectors are not accessible from the back, so the readings will need to be made from the socket side. Some probes are going to be too large to fit in these sockets, so you may need to insert a piece of wire into the socket of which you want to read the voltage of and place the probe on this for your reading. To reduce the potential of creating a short I would suggest taking the ground potential from another connector so that the two wires will remain physically separated.

Caution: It is very important to make sure that you don't allow the two probes to touch each other when taking the voltage readings. This will cause a short which could damage the PSU or other components.

To get accurate readings of the rail voltages it is important that there be a load on the PSU. In order to do this I would suggest downloading Prime95 for this purpose. This program was designed to be used by overclockers to put a full load on the RAM and CPU to determine the stability of their overclocking. Because of this it will put stress on the CPU and RAM which will create higher than normal temperatures. For this reason I would suggest not running this program any longer than is necessary. I would also suggest that an inspection be made of the interior of the case to make sure that there isnít an accumulation of dust which would impede adequate cooling. Pay special attention to the heat sink and fan assembly on the CPU. If there is a dedicated graphics card with a fan installed on it, look at this fan as well.


Readings should not have variances larger than +/- five percent.

Maximum.........Minimum
12.6V.................11.4V
5.25V.................4.75V
3.47V.................3.14V

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#3 dpunisher

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Posted 15 November 2010 - 11:04 AM

Easy stuff first.

Go into BIOs at the earliest opportunity. Verify the time clock is correct (this will tell you if the CMOS batt is OK). Are your settings correct as far a CPU being recognized, it's speed, and are the memory settings/timings correct as well. I have a Gigabyte mobo that would do the reboot 3-4 times when I got my overclock settings a bit too optimistic, and then it would go to default BIOS settings, and then boot normally. Hit the "insert" key when it first starts to see if that will reset all BIOS settings to default, see if that boots on the first try.

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#4 90awdturbo

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Posted 15 November 2010 - 12:41 PM

I had a similar issue with my PC and then realized I had the wrong cable plugged into my PSU to the wall. I agree with the second post thought, check the bios first if u can get in. Your not blue screeing right?
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#5 kjm782

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Posted 17 November 2010 - 07:54 PM

Thanks for all of the suggestions.

1) I don't have a multimeter, although if they aren't that expensive I might look into getting one. I'm sure this won't be the last time that I have a computer problem.

2) Most of the time the computer shuts off before it gets to the point where it would boot from a disk or the hard drive. (A lot of times it is in the middle of the process that detects all of the connected drives.)

3) I shut my computer off overnight last night (about 12 hours). Strangely though when I turned it on today it started up normally on the first try. I checked the clock and it appears that the CMOS battery is ok. Although in the past the only times that I shut my computer off are when I am going to be away for a few days. I'm wondering if that has something to do with it. It will be off for a few days over Thanksgiving so I guess I'll see what happens when I get back.

4) I haven't really messed with any of the overclocking settings. Everything is set at the factory defaults.

5) I am not getting any blue screens. Typically this happens before I even get to the point where the O/S loads.




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