does it show a drive letter in windows explorer?
Or does it show up in disk management?
I cant tell you exactly where to find disk management in XP right now as I booted to Vista.
If in explorer it shows a drive letter drop into a command prompt and type
chkdsk ?: /f
the ? is the drive letter
It may well cough up a error message but could fix it enough to work correctly.
If not type format ?: and it may format it outside of the install process.
If all else fails you may need to redo the partition on the drive.
If your not familier with that write back and you will get advice on how to do it.
I seriously doubt that a power outage caused any damage. It just didnt format correctly and windows is having a hard time recognizing it.