Windows Messenger
I've been having some problems with messenger over the last few days. When it tells me I have email, and I click to go to my inbox, it tells me my password doesn't match that for my email address, and asks me to re-enter it. Also, if I send a message to a mobile, it tells me it needs to shut down. I think this may be if someone tries to reply to the message...
Presumably to re-install it I'd need to go to the Windows Components part of Add/Remove Programmes. This I can't do, as the Windows CD is somewhere at my parents' house.
I'm running XP and IE6.