System won't boot

For a couple years my system sometimes rebooted by itself(random). Sometimes I would go two or three weeks without a reboot, and sometimes it would happen every day for a week. A couple nights ago my screen went black again, as usual, but this time the system did not reboot. The system has power, but it does not attempt to reboot. The LED on the keyboard does not flash like it normally does when the system begins to boot up. I thought the problem was probably the cpu, but I just swapped in another cpu and the system still does not try to boot. I also tried messing with the ram, but as expected nothing helped. I figured I'd still see the bios screen with bad ram. I'm assuming the problem must be with the motherboard. Can anyone think of any other possible problem? Again, the system powers up(fans, power LEDs), but is otherwise dead.

For what it's worth I'm running an old system...
Athlon XP Barton core
Abit NF7-S mobo
9800 pro vid card
1 GB pc3200 ram

Ignore the signature system