Is the message something like "A Disk Read Error Occured. Press CTRL+ALT+DEL to restart?"
There are a number of possible causes for this problem: bad ide cable, bad hard drive, corrupted master boot record or Windows os files are corrupted..
If she has a real windows xp disk, it may be possible to boot from the windows xp disk and using the recovery console get to a point where she can copy her files. Go to site below for instructions on using recovery console:http://www.kellys-korner-xp.com/win_xp_rec.htm
There is an option in recovery console to repair the master boot record: fixmbr
Note that this is very technical and can be nerve racking.
If there is important data on the computer, you and she are not totally comfortable trying this, you might suggest that your friend go to a local computer repair shop and let them try.
If there is nothing of great importance on the computer or in the unlikely event that she is part of the 1% of computer users who actually backup their critical files, then I would try reformating the hard drive and reinstalling xp.
If that doesn't work then it is a hardware problem, either the cable or the drive. Most computer stores have a ide cable for a few bucks and last resort, it's time for a new hard drive.