Fn + power button for diagnostics, computer turns off

I am trying to access the diagnoatics by using fn + power but the computer just powers off. I have tried holding down fn before powering on but it still turns off.

background: computer sat for months without being used, then I turned it on but it will not boot. It displays splash screen, if i hit any key, the progress bar shows loading and it completes but that is as farbas it will go. It will not boot the OS (win 8). It will not boot from a cd. It will not enter bios. It is failing POST from what I can tell. I have tried everything. New hard drive, different ram, took battery out, replaced cmos battery, everything. Looked at all the docs and manuals for troubleshooting and tried all of that. Any ideas what is going on?