system started randomly seizing, now does not boot

Hi Guys -
This was the first system I built on my own about 10 months ago and it worked great until a couple weeks ago. Upon running Bioshock game demo (no idea if related) system seized, i.e. image still on screen but no response/movement from mouse, keyboard, ctrl-alt-del and reset button. I could cut power and start up again and system would run for a while, but then the seizing happened during other applications (e.g. surfing).

When booting up after seizing, startup would load to motherboard/BIOS settings menu with a message that an attempt to overclock had failed (sorry, I don't have the exact wording - I had not changed any settings and had not overclocked anything, intentionally at least). After about six instances of seizing and restarting usually the next day, it now does not boot at all - turning on power activates processor fan, power lights and usb card lights, but no clicking or other indication of doing anything. Before dying I managed to uninstall game and updated Windows and utilities without effect. Any ideas what's going on or how to approach?

Intel E6400
MSI P965 Platinum
WD Caviar SE WD1600JS 160GB SATA
A-Data 2x512 PC2 6400
EVGA GT7600
500W power
Windows XP

Thanks!

 

I can't see the problem clear there, but I suspect the motherboard battery is dried/flat/hwtever. It looked like big watch battery.

Try to check it.