If you have an ethernet 10/100 baseT card installed remove it and try. If not then,,,,
<shrugs shoulders>
I had my pc do the same suddenlt about two weeks ago. It was running fine (which is not the case with you but bear me out) then would not run at all when i turned in back on. After a couple of days of messing around ?I found the ethernet card, or the wake on lan option, was hosing my system up bad. Could not load bios at ALL. Nothing but a breif HDD hit and then a blank screen after a power up.
Good luck!
-Westy