yeah if your computer was running fine for a month that would mean some kind of hardware failing. and since it is restarting during bootup that cannot be a operating system fault.
he said "graphics is Abit Geforce Ti4200", i don't even want to look up that card because it is a fairly recent card which should run at 1.5volt.
your hunch would be the same as mine, motherboard failure. i would not even try to reset the CMOS, just get a replacement from the place you bought it at. also i would consider getting a completly different mainboard model or go with a different manufacturer altogether (ok that may be a bit too paranoid).