Computer hangs when turned on, black screen is all that shows up

[Xdox]

Heys guys heres my specs

Windows Xp
Desktop Computer
Built by myself
USB Keyboard
PS2 Mouse
1.5 GB
Asus P4P800 SE MOBO
e-Geforce 7800 GS video card
Intel Pentium 4 Processor, 3GHZ
Thermatake 420w power supply

Ok, so heres the deal, I built my pc 3-4 years ago with no problems to date, then one day I turned it on and well thats it, it sounds like everything is booting up but the computer just hangs there at a black screen.

The monitor blinks like its idle but nothing will show up. It wont boot into the bios either so idk what to do. So far I've replaced the video card with a working one, replaced the ram with working ram. I've tried taking out the onboard battery while resetting the CMOS? and still nothing. I've disconected and reconnected pretty much every component, including the hard drives. I've tried boothing the computer with the BIOS cd and nothing comes on the screen still. Ive tested the CPU, and hardrive in another computer and they both work fine.

Everything sounds like its booting up, but nothing happens, I can hear the hard drives spinning, see the cpu fan spinning and hear the cpu start up, the power supply appears to be working I guess, I mean everything appears to be powering so I guess its working, the fans are spinning and the lights come on so Im kinda stumped here.

Im guessing its the motherboard because I've tried another PSU from another computer and still hangs up sooo. Thanks for any help guys.

[liondad]

just a note,

Have you tryed on another monitor?
or tryed your monitor on a diffent pc,

[Xdox]

oh yes, i forgot to mention that, I have tried my monitor on another computer and it works fine, and also I got a working monitor from another pc just to give that a shot and it still the same thing. So i guess I have it pretty much narrowed down to the motherboard, would you guys agree?

Thank you

[vahne2k]

If you tried almost possible solutions and the other parts are working well and pnly the motherboard is the problem.. well i guess give it a try repalcing your mother a new one or a spare one...

[liondad]

You dont have a old pci graphic card, laying around or can borrow one,
and try running the system from it,
I feeling I know whats wrong ,
and you need to access the bios to put it right,
i think you are booting up all right and the system is running,
but your graphic card is not loadind its bios defaults at start up,
You need to go in to your bios and see if the AGP/ system is set to auto,
If you can load the sys from the pci graphic card and the pc bios is set to the defaults

You might find its your graphic card thats at fault and its bios is faulty/failed