Did you format the disk when you put it in your friends computer? If so things may be a bit more serious.
My view is XP has a problem with floppy disks though I'm yet to find anything back this up. I've had/seen numerous problems.
Have you tried the disk back in the original computer? If not, are you able to do that - or failing that in a computer not running XP.
There are various recovery software suites arounds so someone may be able to suggest one of those for you.