If it's not too late, can't you use System Restore to roll back to a
time before this problem occured? It looks as if more than just the
registry associations for hyperlinks may have been damaged.

The PC Guru's "Hyperlinks don't work" advice page:
http://www.the-pc-guru.com/Hyperlink...ork_in_ema.php

The PC Guru: www.the-pc-guru.com