Boot into Safe Mode by tapping F8 repeatedly while booting up and then go to System Restore and restore your machine to before this happened.
System Restore is accessible under Start > All Programs > Accessories > System Tools
If that doesn't work try the same boot precedure but select "Last known good configuration" from the menu presented after tapping F8.
Then update your machine to SP3 and there is help with that here: http://community.mcafee.com/message/6631#6631
Always keep your machine totally up to date and make sure you have the latest version of Internet Explorer installed, whether or not you use it. That is IE8.
That's great. Good luck!