That's hard to say: you really have to work on the diagnosis first.
1. Can you boot from a boot CD or (if you have one of these drives) a boot floppy?
2. Can you get into your BIOS settings screen? If so, does everything look okay--in particular, does your BIOS indicate that it can see your hard drive?
3. If you can't even get to BIOS, try taking out your battery while on AC, or, if it's already out, do the opposite and put it in while on AC.