First off I would run the manufacturers diagnostic on the hard drive.
This will be a boot floppy you can get from the manufacturers web site.
You can also try the Microsoft floppy set up as seen here:
http://support.microsoft.com/kb/310994
Requires 6 floppies.
Also try other boot CD's just to see if they will boot.
If the hard drive is still good it could be the IDE ribbon and or Controller.
Anyway the hard drive is the easiest first step to test. CD drive next.