I'm trying to fix my Dad's old Acer, Pentium 4. About 90% of the time, when you hit the power button, the fans scream to life (highest setting) but the system won't boot. No display, not even the BIOS screen. There is power to the devices, I can open the CD tray, but no lights. If you shut it off from the power source, and keep trying eventually it boots up okay, and almost silently. I think it may be the temperature sensors, thinking it too hot triggering the fastest level CPU fans then shutting down. Any Ideas?