|If you have made no changes inside your case to the connections or jumpers on/of your hard drive and have not been fiddling with it's cables since it last worked, you have not been fiddling with settings in your bios Setup, and your computer works okay up until the point in the boot where it it is supposed to recognize your hard drive, and it works okay with bootable floppy disks.........|
On another computer go here and download the Diagnostic utility, execute it to make a bootable floppy disk, and test your drive on your own computer:
If your drive passes both diagnostics tests, there is nothing wrong with it - something else is wrong with your computer.
If your drive does not pass both diagnostic tests, it is failing or has failed completely. You may or may not be able to recover data from it.
If you're not sure whether your computer is booting properly, lots of things can cause your hard drive to not boot up - there may be nothing wrong with the hard drive. The most common reason, if you haven't been fiddling with the things mentioned above, is a failing or dead computer power supply.
If your computer will not work with the bootable diagnostics floppy, connect the hard drive to another computer and test it on that computer.
If you try booting your drive connected as master on the other computer without using the bootable diagnostics floppy, if it seems to work okay, don't boot all the way into Windows - Windows will try to set itself to the hardware on the different mboard. On the other hand, if the hardware is different enough from your computer XP may not start up - that does not necessarily mean there is anything wrong. You can connect your hard drive as slave on either IDE, or master on the second IDE, on the other computer, to see whether you can see whether it's contents can still be seen properly.