Hi len84pa,
1. Have you made any recent changes on the computer?
Method 1
Run the fixit tool available in the below link and check if it works.
http://support.microsoft.com/gp/system\_maintenance\_for\_windows
Method 2
If the above step fails then check if the issue persists in the safe mode with networking
Steps to boot to Safe mode with networking
a) Restart your computer if it is powered on.
b) Tap the F8 key after your computer initially powers on.
c) Once you see the Advanced Boot Options menu you can stop tapping.
d) Use the up/down arrow keys to highlight your selection.
e) Select Safe Mode with Networking and press Enter.
f) You should see drivers loading, and then Please wait.
g) You should then be at the Welcome Screen.
h) Logon to your computer using an account with Administrator privileges.
Method 3
If the issue does not persist in the safe mode with networking thenthere is a possibility that some third party programs installed on the computer is causing the issue.
I would suggest that you perform clean boot and check.
To help troubleshoot error messages and other issues, you can start Windows Vista or 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.
Refer the below link to know more about clean boot procedure.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
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:
a) Click Start, type msconfig in the Start Search box, and then press ENTER.
b) If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
c) On the General tab, click the Normal Startup option, and then click OK.
d) When you are prompted to restart the computer, click Restart.
Hope this helps!
Halima S - Microsoft Support.
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