Hi There
You have video output so your power to modbo, video card and CPU is OK.
Does you video card need it's own power from the psu, check to see if it's got a molex connector.
If not forget about that bit.
Can you boot to Floppy disk or CD ?
Unplug your RAM re-boot are you getting post beeps?
If you do plug your ram back in and assume ram is OK
Make sure if you have x2 512mb ram you have two idential sticks, if 1gb stick forget about this too.
Go into bios and turn off "Wallpaper" It's not called wallpaper but I forget what it is called in bios.
reboot can you see any error messages?
Is you bios set to auto detect for your drives, most mobo's are set to auto detect but check anyway.
I had similar problem today, (funny eh) and it was a bad stick of ram.
Is is possible you can test with another stick?
Anyhow let us know how you get on
steve