Compuer boot and hard drive problems

My computer will start to boot, go to the “Your computer turned off unexpectedly… please choose mood. (normal, safe mode). Then i choose one, and it continues to boot. Then after ten seconds it re-boots. I tried my DOS boot disk and found out that it can’t find my Hard drive. Last time I shuted it down, I did it improperly. Could I have possibly erased my Hard drive? What do I have to do?