Hi,
Method 1:
Refer the link and follow the steps.
Windows Vista or Windows 7 no longer starts, and the Startup Repair tool does not fix the problem
http://support.microsoft.com/kb/934540
Method 2:
Refer the link:
Visit the link provided and perform the steps and check
How to use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windowshttp://support.microsoft.com/kb/927392