Stuck on HP screen

I was playing sims 3 the other day. Sometimes i get errrors saying that there was a problem with the graphics card. Usually this is solved after alt tabbing and waiting a while. However, this time, the game froze, and I had to force the computer to shut down. When I started up the computer again, it got stuck at the welcome screen. I tried pressing f10, esc, and everything else but those do not work. I reset the CMOS, took out the battery, and reseated the RAM, with no results. Finally, I tried booting after disconnecting the hard drive, and I was able to go into bios. Of course, I couldn't boot into Vista. I don't have a recovery disk to reformat the hard drive...WHAT SHOULD I DOOO?