Yesterday, my PC began having an unusual problem. Upon starting up, the power LEDs and fans came on, but nothing else actually happened. At all. So, I took it apart, checked all the connections, put it back together, and tried it again. It was working again, and it worked for the rest of the day.

This morning, I try to turn on my PC again. This time, the LEDs and fans come on, then turn off for a few seconds, then turn back on again, but still nothing else happens. What the heck is going on?

It is a desktop PC I built myself with a barebones kit this last February. These are the parts inside it:

Shuttle SG31G2 Intel Socket T(LGA775) Intel G31 2 x 240Pin Intel GMA 3100 256bit 3D engine with a powerful 400MHz core and DirectX 9.0 glamor small form factor Black XPC Barebone

Crucial 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 667 (PC2 5300)

Seagate Barracuda 7200.10 ST380815AS 80GB 7200 RPM 8MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive

And Windows XP SP3.
Any help or insight you could offer would be great. Thanks!