My Optiplex 760 won't boot up or show BIOS

[Benjamin_Skald]

It powers on and the PSU test light is green, it doesn't make any noises except for the fan and the front power button is amber.

I've cleaned it, reseated the ram and CPU units as well as reseating all PSU power cables.

I have no idea what could be wrong so any input is appreciated.

[JOcean]

The system is 10 years old and it is possible that the CMOS (coin cell) battery is bad. Try changing the battery and be sure it is a new battery not one that may have been hanging around in a drawer. I am not sure which form factor system you have but this link is for the MT. Another possibility is that though the PSU seems to test good it may be bad. Only installing another PSU would confirm yours is working or not.