It sounds pretty serious when you cannot even get to the BIOS screen. Perhaps a drastic failure on the motherboard.
One thing you might try is removing and replacing the cmos battery on the board. This should reset the defaults, if that is still viable.
Make sure all the memory modules are firmly seated; and you may want to carefully remove and reseat the cpu itself, if nothing else is helping.
Do not try to start it up without good heat sinking though.
http://www2.lacitec.on.ca/users/9800776/help/fixingpccrash.htm#blankscreen
Since the problem is most likely with the motherboard rather than the hard drive, the data on the drive should still be good, and could be recovered by connecting it to another system.
One thing you might try is removing and replacing the cmos battery on the board. This should reset the defaults, if that is still viable.
Make sure all the memory modules are firmly seated; and you may want to carefully remove and reseat the cpu itself, if nothing else is helping.
Do not try to start it up without good heat sinking though.
http://www2.lacitec.on.ca/users/9800776/help/fixingpccrash.htm#blankscreen
Since the problem is most likely with the motherboard rather than the hard drive, the data on the drive should still be good, and could be recovered by connecting it to another system.