Did you ever install a new program and find that your computer suddenly ground to a near halt? Or your web browser quit working or the computer will only boot in Safe Mode? A possible solution is System Restore.
System Restore, for Windows machines, is like a big UNDO button for your whole computer. It must be enabled before you have a problem though, or it won't do you any good.
If you have System Restore enabled (right-click on "My Computer," click "Properties" and go to the "System Restore" tab to turn it on), each time Windows performs an update or it will automatically create a "Restore Point" before making changes. These restore points allow you to revert your system back to a time when everything was working. If a system update causes a malfunction with your computer, this will undo the update and allow you to get back to work.
You can also go to the System Restore tab and create a restore point yourself if you are about to make changes to your computer that you think might cause a problem.
To restore your computer to an earlier time, go to Programs | Accessories | System Tools | System Restore. You can then select a restore point that was made on an earlier date when you know your computer was working.
System Restore will not delete any data, it only affects system files. And it may not always fix the problem, but it is a good tool to learn how to use. Do yourself a favor--turn System Restore on right now.