Monitor shut off, no BIOS post, no keyboard or mouse lights, will not boot

I was working on my computer when the monitor suddenly shutoff. I did a manual reset and now the monitor will not turn on and the BIOS will not post. After trying several things, the BIOS posted once, and now will not post anymore. Any help ASAP would be great! Thanks!!!!

System specs
P4 3.4 Ghz
Gigabyte GA-8KNXP motherboard
3 GB RAM
X800XT video card
XP Pro