To do a System Restore follow these steps:
Click Start and then to All Programs
Scroll to Accessories and then System Tools
Click on System Restore
A Welcome screen will come up and you need to click on Restore My Computer To A Earlier Date
Then click on Next
Now you will see in the window Select A Restore Point. From here select a date a couple of days before the problem started.
Then click Next
On the Confirm Restore Point Selection window verify the Restore Point you chose is correct.
Close all open programs and click Next
The computer will now automatically shut down and reboot. When it restarts you will see ”Restoration Complete” page and then click OK
Once you have made sure that everything is now running correctly then please reply back with the results.
If this does not work then follow the next steps to do a Repair Installation