GPU problem!

I'm using on board graphics right now because anytime I put in an AGP video card into my AGP slot I turn on the computer and the screen doesn't go on.
I don't know what to do it worked just before with my radeon 9200 but not now and it won't work at all with my geforce 7600 gs.
Any tips?

How power your system pushing? And how old is your pc?

I got a 550W PSU if that's what you mean. I bought this computer about 3 years ago, it's a Pentium 4 3.0.
I think the on board graphics got disabled too or something, when I turn the computer on after the Windows XP loading screen it just goes to a black screen but the light is still green, you could even hear the Windows log on tune with the speakers on.
I'm using another computer for now because the screen won't show anything with a graphics card or on board graphics.
Everything is working fine except the screen won't show anything other than the XP loading screen.
What's the problem and what can I do?

Ok you need to check on the compatability of your agp slot.You need to find out if it supports agp 3.0 or 2.0.This does make a difference.Let us know your full system specs.

Dahak

AMD X2-4400+@2.644 S-939
EVGA NF4 SLI MB
2X EVGA 7800GT IN SLI
2X1GIG DDR IN DC MODE
WD300GIG HD
EXTREME 19IN.MONITOR 1280X1024
THERMALTAKE TOUGHPOWER 850WATT PSU
COOLERMASTER MINI R120

Did uninstall the drivers in windows for your old card and install the new cards drivers? What do you get in safe mode?

Holy smokes.
I solved the problem but it took a really long time.
Everything was connected fine just after the XP loading screen nothing happened.
I tried running it in safe mode and it would keep hanging at agp440.sys.
I used the recovery thing and tried safe mode again and it hung at a different thing. I kept doing that about three more times but it kept hanging at a new location.
I instead just brought out my Windows XP CD and put it in except the computer wouldn't boot to it, I had to disconnect the harddrive and start up the computer to the CD. After it boots to the CD I reconnected the hard drive and reinstalled windows.
It started up fine except there were some missing drivrers for the intergrated audio and a missing ethernet controller so I couldn't get any updates. I had to run over to a friend's house, download the drivers onto a CD.
I have to reinstall everything now but it's better than having a nonfunctional computer. Thank you to everyone who gave any advice and my name is pronounced boo-thed.