I have a five year old home built box that hasn't been moved or opened for over 2 years. It ran fine and shut down normally last night. Today when I turn it on, the machine POSTs, loads Windows up to desktop, then the screen goes blank. I here a soft click sound but the fans keep running and peripherals like the mouse and network card remain lit (although the lights on the network card indicate no trafick).

I opened the box and cleaned out a couple dust bunnies and made sure the fans were all clear. All of the cards and connectors are firmly seated. I try to start again and it doesn't completely make it through load to Windows desktop before screen goes black again. Lots of cool air and no burning smells. Nothing seems unusally hot.

It's a 2.6 GHz Pentium 4, 1.5 GB RAM with 40 GB of free hard drive space, running XP SP2. It just had it's weeking full scan on Sunday. I'm thinking something is shorting out or I have a micro crack someplace that doesn't take much heat before causing a problem.

Any ideas on what to replace first? Any suggestions are very much appreciated.