Computer keeps turning off after turning on

Today, I decided to dust my computer like I usually do but when I hooked everything back up the computer turns on for 3 seconds and turns off and it was working the day before. I see the POST screen for a few seconds before it turns off, and I don't have a spare mobo/psu to test with, and I don't really want to spend money for a multimeter/psu tester since I doubt I will be using those more than a few times at max since this is my first encounter with this type of problem ever. Is there any other ways to figure out whats wrong with my computer or what would you recommend me do in this situation? I have tried switching ram slots and tried draining the power completely by disconnecting the power cord to the computer and letting it sit there for a few minutes and pressing the on button without the power cord connected.

Edit: I used to be able to see the POST screen but I don't anymore.

Edited by LearningDrone, 25 August 2010 - 02:17 AM.

LearningDrone, the first thing that comes to mind is that you have inadvertently dislodged something when you cleaned the computer. Go back and check every connection and the seating of all cards and modules. Physically disconnect and reattach these items.

I've thought of that too but I'm too scared that if I disconnect something, I won't figure out how to put everything back together, any tips for a novice like me?

First, open the case, this may take some thought as some manufacturers can be devious about the way to open the case.

Second... before you touch anything inside touch the metal case to discharge any static electricity, this could kill chips on the boards, or RAM modules.

The motherboard is the largest component in the case, this is where most everything plugs into. On this board will be a fan and heat sink, this is what you wan to look at. If there is a build up of dust, purchase a can of "canned air" from you local electronics store and blow it out. If there is a heavy accumulation of dust, you may need to use something like a Q-tip to clean the surfaces of the heat sink and fan.

I disconnected and reconnected everything but the same problem still occurs.

Reseated all the cards and RAM? disconnected and reconnected all of the power cables?

If you do these one at a time you shouldn't have any problems with confusing where things go.

Edited by dc3, 25 August 2010 - 07:43 PM.

Yep, that's the way i did it. Not sure if this is related to the psu or some malware but my computer would randomly reboot when the room temperature above 67°F but not always as it has rebooted itself when the room was only around 63°F. There was no specific timing and I don't heat was the issue because the cpu temperature was only around 131°F when it restarts. I was planning to reformat my hd after dusting my computer to confirm if it was a malware or not but I just lost that chance

You did not mention what you meant by “dusting the computer”. You opened the case and dusted the inside? What did you use to dust it? (Be careful when dusting the inside of a computer; one time when I tried cleaning my motherboard, I broke off an SMD capacitor which was next to impossible to solder back on.)

I agree that it does indeed sound like one of the PSU’s cords got disconnected (or worse, partially disconnected). There are only a few cords from a PSU, so it should not be difficult to check them. There should be one long block that has only one place to connect to on the motherboard and one way it fits. There should be another smaller one that again fits only one place in your system. Then there are the cables that connect to the drives. There aren’t really many ways to mess up connecting the PSU. It really is worth your effort to reconnect the cables (while the PSU is switched off of course). Besides, nobody said to disconnect everything before reconnecting them, just go through each cable and disconnect then reconnect it, one at a time. That way there is no way to mess things up.

Yep, that's the way i did it. Not sure if this is related to the psu or some malware but my computer would randomly reboot when the room temperature above 67°F but not always as it has rebooted itself when the room was only around 63°F. There was no specific timing and I don't heat was the issue because the cpu temperature was only around 131°F when it restarts. I was planning to reformat my hd after dusting my computer to confirm if it was a malware or not but I just lost that chance

I seriously doubt that this problem is related to an infection. The fact that this is coincidental to your having just cleaned the computer prior to this trouble starting really points to a bad connection.

Did you take the fan and heat sink off of the processor while you were cleaning?

Edited by dc3, 25 August 2010 - 08:36 PM.

I'm using the stock intel heat sink/fan for my processor and when I tried to take it off by turning the 4 black knobs, the heat sink and fan was loose but I didn't take it off since I didn't know how much pressure was safe to attempt to take it off. Then I thought that I never had to really take it off before for dusting since I would usually just brush off the dust that builds up on it so I just pushed the knobs back down and locked them up. And when I said about disconnecting everything eariler was that I meant everything connected to the psu and I did reseat my graphics card and ram.

Edited by LearningDrone, 25 August 2010 - 10:57 PM.

If the heat sink was loose from the CPU I would pull that heat sink and fan off and reapply the thermal compound. You will want to clean both the top of the CPU and the heat sink. You can use a credit card to carefully scrape off the old compound, you can use alcohol to finish cleaning the two surfaces, try to keep the alcohol away from any other surface of the CPU other than the metal on the top. That metal part is called the heat spreader.

When you go to apply the thermal compound you only need a small amount, about the size of a grain of rice. Apply it to the metal surface of the CPU and spread it evenly, then put the heat sink on.

Arctic Silver 5 is a good brand of thermal compound. You can get it at most any electronics shop, even Radio Shack.

At the Arctic Silver 5 web site there are specific instruction for your CPU, if you think you will need them.

http://www.arcticsilver.com/instructions.htm

Edited by dc3, 25 August 2010 - 11:43 PM.

I was looking at youtube videos about this and I was wondering if I can do this without having to take the mobo out of the computer case?

Yes, you should be able to do this in the case. Just be careful when you go to refasten the heat sink, don't flex the motherboard any more than you have to.

Just a question before I go out and buy the thermal compound, If it was really a cpu/heatsink problem, wouldn't it be able to last more than 2 seconds, or a least get a glimpse of the post screen, before the cpu overheats and turns itself off?

Maybe, maybe not. A modern CPU can go from room temp. to >100°C in just a few seconds without a heat-sink, that’s why there are warnings to never run a CPU without a cooler of some sort. So it depends on how much heat was being removed from the CPU. It sounds like it was heating up fast enough that you couldn’t get even that far, so I would advise against running it again until you’ve gotten it set up correctly. (Had you tried blowing at it with a fan or turning the A/C on or something to see if temperature does affect it?)