Your OS has become corrupted and needs a repair install or you have a virus that has caused corruption
If this started very recently you may be able to perform a restore.
If not then follow these steps (even if you already fixed it):
First go to download.com and download tuneup utilities 2007 and run the registry fix.
Then go to ccleaner.com and download and run its program
If that didnt work download and install a free version of AOL and its security. Or download Kaspersky Internet Security.
Make sure you don’t have any other protection running and if you do unless it is norton or one of the ones I mentioned it does not have as high of a detection rate.
Next update the security program and go to Safe Mode by pressing F8 repeatedly (every second) after the computer first shows a screen after restarting.
In safe mode hit YES after logging in and run the protection software on the pc (spyware and virus scan)
If you still see these problems then run a repair install on your computer after you back up your important data.
You do this with your disk that came with the pc.