Hi,
Have you made any recent software changes on the computer?
Method 1:
Step 1:
I would suggest you to start your computer in
safe mode and check if the issue persists.
Start your computer in safe mode
http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode
Step 2:
If the issue still persists then I would suggest you to perform a
clean boot.
Clean boot:
This could be happening if any of the background programs is conflicting with the smooth running of your computer. To help troubleshoot error messages and other issues, you can
start Windows 7 by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/kb/929135
Note: After you have finished troubleshooting, follow step 7 in
the article to boot the computer to normal startup.
Method 2:
You may also perform
a system file checker scan.
Check the below mentioned link for further guidance on
System File Checker scan –
http://support.microsoft.com/kb/929833