|If there is information (files, data etc...) on the drive that your friend would like to preserve then do NOT go anywhere near reformat or re-installation routines - yet.|
Essentially follow the links and advice from Johnw (and others) re' testing the drive fully, recovering that data - first.
If you're successful in that regard, and verified the data recovered onto optical media is truly accessible on another working system, then you can consider a couple or more options.
1) Use the recovery disk routine - or the recovery partition (if it exists and is usable).
2) Try a true repair installation - effectively an over-write of the current installation; but you will need either a full (or Upgrade) version of the OS.
If an overwrite fails then a parallel installation (again a full/upgrade disk is required); after-which you can later delete the original version, having verified you can still access data etc - and ideally again copied safely elsewhere.
3) wipe the drive (reformat etc. the c: partition (do NOT wipe the hidden one at start of drive - if it exists) and then use the recovery disks etc....
If the drive is effectively burnt toast (duff, dying, or actually dead as in the parrot on its back with feet in the air) then obviously you will need to replace it. And then you have to resolve the issue of any missing (and usually required) hidden partition that was on the original drive - but isn't on the new one...? Recovery disk routines usually refer to that hidden partition if I recall correctly.. If it isn't there then you need to resolve that issue. If this becomes the case... post here for more input there...
A long shot - and it is very...; a recovery console approach "may" enable you get it going again - as in getting back to a resotre point prior to problems arrival. But I'm not sure you can even get as far as invoking recovery console?
There is also a winternals recovery/repair disk around that may actually do what's required...; more on that subsequently... Whereabouts are you located?