This sounds like malware so I moved it accordingly.
You don't state what operating system and service pack you are using but I trust that whatever it is, it is up to date.
Try booting into 'Safe Mode' by tapping F8 repeatedly while booting up and when there try to initiate a System Restore to before all this happened.
You should find System Restore in Start/All Programs/Accessories.
If that is successful please temporarily disable System Restore to get rid of the infected restore point.
Then update your system and update McAfee and anything else that needs it.
If you could give more information as in line 2 I can hopefully help more.