Hi,
Thank you for posting in Microsoft community.
1. Since when are you facing this issue?
2. Any recent changes made to the computer?
Method 1:
Check if you are able to boot in safe mode or not:
http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode
If yes, I suggest you to put the computer in clean boot state and check.
To help troubleshoot error messages and other issues, you can start Windows Vista 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 link below for more details: https://support.microsoft.com/en-us/kb/929135/en-us/
Note:
After you have finished troubleshooting, follow these steps in the above article to reset the computer to start as usual.
If not, try performing a startup repair and check:
http://windows.microsoft.com/en-US/windows7/What-are-the-system-recovery-options-in-Windows-7
Method 2:
If not, I suggest you to Rebuild the BCD store manually by using the Bcdedit.exe tool.
Refer step 3 to do the same in the below article:
**http://support.microsoft.com/kb/2004518**
For your reference:
Hope this helps.
Please reply to us with the status of the issue.
Thanks.