First make sure it works without the drive connected.

Then work trough possibilities.
The data cable - Try another one.
- Is it on one pin down or sideways?
- are any of the pins bent?

The hard drive - Is it jumpered correctly. The jumper settings are commonly marked on the drive
- If you have any other devices, like a second hard drive, or DVD, disconnect them.
-Try another hard drive.

Other drives - If any, try disconnecting them. Both Hard and CD/DVD.
- Check the jumper settings on them.

Motherboard - Try it on the other IDE connector. It might to be on IDE 0.
- If it is try the other. IDE 0 may be faulty and depending on the bios IDE1 may work.
- Are there any cards installed. If so remove them and try the drive.

Power supply -Try another one if you have one.
-If not, confirm the 5V +/- 0.25v and 12V +/- 0.5V are correct.

I think that covers it, except to try removing and installing the memory, and making sure thr modules are correctly seated.
If you are really desparate, you could also try removing and reseating the processor.