Method 1: Boot the computer in safe mode and check if the same issue occurs.
http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode
Method 2: If the issue does not exist in Safe Mode then try to set your computer in Clean Boot state.
By setting your system in clean boot state helps in identifying if any third party applications or startup items are causing the issue.
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 clean boot troubleshooting step, follow the steps outlined by “How to reset the computer to start as usual after troubleshooting with clean boot “in the provided link to return your computer to Normal startup mode.
For any Windows related issues please feel free to contact us and we will be glad to help.