Shut the pooter down.
Restart the machine and hit F8 while it's booting up and select advance boot options, then Safe Mode. (You could log on as admin, but i'll assume for this that isn't available to you.
Click on 'what is system restore' and use System restore to roll back your machine.
You don't mention what operating system you have so I've assumed Vista or 7
Let us know how you get on
