Hey,
Got a pc the other day...a compaq p4, etc. It boots up, the hard drive runs, the disk drives are operating, everything seems to be fine, but the monitor is not getting any video signal so it just goes to standby after 5 seconds. I've tried 3 other video cards and nothing works, the second I plug in the monitor cable the monitor goes active but then loses signal again, same when I unplug the cable...can anyone point me in the right direction? I've tried agp video and pci video cards also...nothin....what is shot here? Is this thing just dead?
Sorry if this is a vague dumb question...

On Compaqs, there can be two video cards- one on the motherboard, and one on the agp/pci slots.

Check to be sure you're using the right port to hook your monitor to.

Also, can you verify that the monitor picks up a signal from a known good machine?

well if you just bought it the other day take it back and tell and ask them wtf is this? Otherwise I can't think of anything right now, I had a very similar problem before but it was my mobo it came out the box 3 times jacked up #1 straight BLEW UP my PSU #2 The crap that's happening to you along with rebooting over and over #3 Fried my processor so bad it was smoking!!! I will never EVER in my life purchase a Gigabyte mobo EVER AGAIN. Have any of you ever seen a good PSU blow up? It's pretty neat different colors and what not. But when it's over your just extremely pissed

nah, didn't buy it the other day...it's a neighbors pc and he wanted me to clean it up, etc...problem is, can't even get into the computer...no screen, etc.

Goalie...it came with a GeForce mx card in the agp slot, and it was working before, but crashed apparently...

Oh yeah, and my monitor works, I have 2 working ones and they both work just fine on other machines..
There's only one monitor hookup, and it's the agp slot card...

Any suggestions on how to test what is wrong?

I forgot to mention that when I checked inside the case, it looked like the Planet Degobah in there. I had to take off the cpu heatsink and use condensed air to the the caked dust off of it....I'm thinking maybe the cpu may have gotten fried...the psu is supplying more than enough power...I think it's a 350watt....
anyways, I'm gonna try to clean the cpu a bit tonight and reseat it to see if that does anything.....
another thing I guess I could do is remove all the RAM and boot up to see if I get any error beeps, etc. I dunno....in the dark here.

Update

Swapped out the CPU with a 1.7 P4, I had laying round the house. Booted up, monitor came on. Everything is working.
Reformatting their drive now...and will be returning my first PC job with pure satisfaction