(A). Try performing hardware clean boot and check.
Here’s the procedure to do it:
1. Go to start and type device manager in the start search field.
2. Type device manager and select device manager from the programs list.
3. Right Click on Sound Card, Video Adapter, and Network Adapter one by one and click disable.
4. Reboot the computer.
If this fixes your problem, enable to hardware devices one at time to find the exact device causing this problem.
After you found the device that causing the problem you can resolve by installing last driver or replacing the device.
(B). Perform normal clean boot and check.
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. Clean boot will stop any interference with other third party software on the computer.
Steps to perform clean boot:
1. Click Start, type msconfig in the Start Search box, and then press ENTER to start the System Configuration Utility. If you are prompted for an administrator password or for a confirmation, type the password, or click Continue.
2. On the General tab, click Selective Startup.
3. Under Selective Startup, click to clear the Load Startup Items check box.
4. Click the Services tab, click to select the Hide All Microsoft Services check box, and then click Disable All.
5. Click OK.
6. When you are prompted, click Restart.
7. After the computer starts, check whether the problem is resolved.
If the issue is resolved check which third party is causing the problem, referring the link given below:
http://support.microsoft.com/kb/929135
Reset the computer to start as usual
After you have finished troubleshooting, follow these steps to reset the computer to start as usual:
Click Start, type msconfig.exe in the Start Search box, and then press ENTER.
If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
On the General tab, click the Normal Startup option, and then click OK.
When you are prompted to restart the computer, click Restart.
Hope it helps