Try clearing CMOS.
If you don't know how, do this:
unplug the computer from the wall, press the power button to discharge any remaining power in the PSU. Now open up the computer, locate the coin battery (will be silver/in a slot on the motherboard). Take that out for a few minutes, reinsert it, and then power the computer back up. See if it boots that way. If it doesnt, you may have to look online on Dell's website to see if you have to use a jumper to short out CMOS pins (should be soemwhere on Dell's site for that computer model; I know HP has instructions for it on most of theirs).
If you get the computer booted up, and still think its a virus, go through this guide: http://www.techist.com/forums/f51/sp...osiris-165828/
If possible, check temperatures of the CPU with CoreTemp (google for it). Could also try blowing the dust out of the PC with compressed can of air, or a regular air compressor (if you have access to one).