Hi all. My son had problems installing/uninstalling a game. Now all files have the .lnk extension. Can't system restore. Can't regedit. Can't reinstall XP. All disk based and downloaded programs give the same result. Any ideas will be gratefully received.

You can try System Restore from Safe Mode or from the Run... command:

%SystemRoot%\System32\restore\rstrui.exe

Or see if this helps:

Go here and download the LNK fix
Read the instructions at the top of the page first.
http://www.dougknox.com/xp/file_assoc.htm