Check the power connectors and replace the IDE/Sata cable with a known good one. If it is an IDE Drive connect it to the secondary IDE channel to rule out faulty IDE Slot. Check the BIOS to see if the Hard drive is detected properly and also check that it is in the Boot list.
You can use the Hard Drive Makers Testing Utility to Test the Drive which can be downloaded from below.
Hitachi / IBM
Western Digital
Fujitsu
Seagate
Samsung
If the Hard drive tests out OK you can Boot from your XP CD and enter the Recovery Console to run these commands.
Insert your XP CD and when you see ?Press any key to boot from CD? press a key. Now wait for the XP installer to finish loading up and you will be presented with the option to press R to Repair.
Press R.
The next screen will ask you which Windows? installation you would like to log on to. Normally the following will be listed:
1: C:\WINDOWS
Press 1, then Enter to continue.
You may now be asked for the Administrator password. If you know this type it and press Enter. If you don't know the Administrators password it may be blank. Just press Enter or type your username and password.
At the command prompt type these commands:
chkdsk c:/r and press Enter 'let it run through the five stages'
fixmbr and press Enter
fixboot and press Enter
Wait until you are returned to the Recovery Console.
Type bootcfg /rebuild
Once you are back to the Recovery Console remove the XP CD and restart your PC.
If you have data on the drive that needs to be saved and it isn't corrupted you can remove the drive and Slave it to another System or invest in a USB Drive enclosure. You could also boot from a Linux CD to save the information.
For Data Recovery you can use use OnTrack Data Recovery
http://www.ontrackdatarecovery.com
