IF you re-install then you will lose all your data...
That's only true if you opt to re-format the hard drive, which doesn't have to be done - you can just re-install the OS and leave the rest of the disk intact. I know it can leave Windows in a bit of a mess, but he could then hive his data off to DVD and then do a re-format.
But as others have said, try a repair first. It often doesn't work in my experience, but it can do no harm to try.
yeh, windows repair is lame.