BleepingComputer.com: no signal,yellow light on boot, psu tests good

When the computer was shut down last night, all was well. This morning, turned power on and got a "no signal" message on the monitor. The fans power up, a yellow light comes on the front panel and I hear 1 beep and the dvd spins. Then the monitor goes into sleep mode and the fans keep running.
Here's what I have already tried:
1)tested the psu with a tester, all tests ok.
2)tried taking out the ram and running with only 1 or the other, then reseated them both.
3)tried taking out the graphics card (XFX GeoForce 7800GT 256mb) cleaned out the dust and reseated it.
4)checked all connections to monitor, computer, power connections etc.
5)disconnected power and then held down power button for 15 seconds and tried re-powering up.

nothing has made a difference. How can I test the MOBO? Also, is there a test for the hard drive?

The computer was experiencing freeze ups a couple of days ago. It would just freeze and need to be rebooted before it would respond.
so we took off the fan over the heat sinc and cleaned the dust collected there.
We didn't take the heat sinc off, just the fan. generally cleaned all the fan intakes/exhausts etc... was very careful.
Then the computer was working fine for a couple days before this problem.

Does anyone have any advice or suggestions?
windows xp sp3
asus k8n-vm mobo
7800Gt Xfx Geoforce 256MB
Thanks, Brenda

Hello Brenda and welcome to Bleepingcomputer.

Since your computer is not displaying any video, I am not sure if running a hard drive disk diagnosis utility will be very useful at this point.

But here is a link to a list of tools for hard drives.

http://www.bleepingcomputer.com/forums/topic28744.html

I am a bit confused as to what you mean by the monitor goes into sleep mode

Does this mean that at some point during the POST you do see the BIOS screen?

As for testing power supplies, the only cheap tool to use is a VOM meter and a complete understanding as to the outputs of each connector.

If you really want to do this, here is a link that shows the various plugs and their outputs.

http://www.playtool.com/pages/psuconnectors/connectors.html

It is sounding to me like one of your power supply rails may have failed, there are 3.3 volt 5.0 and 12 volt rails built into power supplies.

Cooling fans use 12 Volts, video cards use 3.3 and some use 5 volts.

If the 3.3 or 5 volt rails have failed, the computer may still exhibit some signs of life, such as the case fans spinning.

If your monitor is NOT the problem, you may want to look into replacing your power supply.

I seen where you mentioned you have one system beep during start up.

That beep usually indicates an "all is OK" status, which I find strange, this would not be the case if a rail has indeed failed.

Please make sure the monitor is in fact okay by placing it on another computer.

You may also want to recheck that the video card is not the issue, by placing it into another computer, or trying a different video card in your computers slot.

Bruce.

This post has been edited by MrBruce1959: 03 April 2011 - 09:55 PM

The above post is very useful. My first thing would be to take a close look at the motherboard and video card capacitors, if you see any that are bulged at the top, the they are bad and the board will need replacing. A bad power supply can cause the caps to go bad, so checking the voltage output would be my next step. I'd also pull all non-essentiald such as modems or any other cards. Since everything is spinning up, that means the power supply is comming online. Use a voltmeter to check the 12 volt and 5 volt rails with it powered up. On a spare plug from the power supply, look for 5 volts +/- 1/2 volt between the red and black and 12 volts +/- 1/2 volt between the yellow and black. If your volt meter probe is small enough, you can probe the orange wire on the plug feeding the motherboard for 3 volts +/- 1/4 volt. If it's not within range replace the power supply,If all that is good, try swapping monitors then Video cards (you can find a cheap $14 PCI vid card at Tiger Direct for testing here )

This post has been edited by Flabum: 03 April 2011 - 10:27 PM

Hi,
The monitor would show nothing on startup, then right after I heard the beep, it would go from a green on light, to an amber standby light, then give a no signal message and go dark.
I used info from both posts, and rechecked the psu. It all checked ok. I disconnected the graphics card and plugged the monitor directly into the on board video. The computer is now working as usual, though my son's games don't run as well. I guess it is the graphics card then. Are these cards repairable?
Thanks,
Brenda

It could be corrupted drivers, remove the video card, uninstall all the drivers and software related to that card and try re-installing it. If you get no video from it when you re-install it, then it's bad.

This post has been edited by Flabum: 05 April 2011 - 09:15 AM