|If you cannot get into BIOS at all, it could be:|
1- Bad BIOS setting: Clear CMOS, Reset Defaults, then tweak BIOS settings
2- Bad Memory Stick: If 2 sticks, try one only, then the other one only. Run Memtest from bootable CD to verify problem.
3- Possibly Power Supply is dying and is not supplying all voltages any longer: swap in another power supply to test.
4- If CPU heat sink was disturbed: remove heat sink, clean surfaces and apply the correct amount of thermal compound. Ask for details/supply CPU model.
5- CPU fan is not working or is unplugged: Verify it is plugged in and spins when turned on.
Possibly others. Please supply full details on your equipment and results of above testing.
You have to be a little bit crazy to keep you from going insane.