My knowledge on the subject is limited, but the BIOS might be a good place to start. On my computer (Dell Dimension 4700 running Win XP), in the boot set up I have the option to set my computer to turn on at a certain time on particular days of the week. Also, you could try disabling the "auto-boot computer after power falure" option. This will solve any problems with faulty wiring or the power supply.
"We can categorically state that we have not released man-eating badgers into the area."
-UK military spokesman Major Mike Shearer