If you're running on windows vista, which is the OS that I most often see this issue on, try the following:
Turn off your computer. Turn it on and begin tapping your F8 key once every second until you see a list of options appear on your screen. The very top option should be "Repair your computer". Select it and press enter. This will load the recovery environment for your computer. If you are prompted for a username and password, select your username from the drop down menu and then type in your account password.
On the next screen, select "System Restore" (NOT system recovery). It will then load the system restore utility (this may take a minute), and will prompt you to select a point in which to restore your computer. Select a date that you know you weren't having this issue. Try not to go further back than a couple months because you can start to see problems if you go back too far.
Follow the steps to complete the system restore--then make sure the first thing you do is all your windows updates.
Good luck! =)