Step1: Insert your windows 7 installation disk into the optical disk drive and restart your computer.
Step2: When window will give the option “Press any key to boot from CD or DVD” then press any key and wait for windows to load the files.
Step3: Select language, time and keyboard or input method at the ‘install windows’ screen and click next.
Step4: click on the option ‘repair your computer’ at the bottom of the next screen.
Step5: Click on the radio button next to "Use recovery tools that can help fix problems starting Windows" option and select your operating system. Click "Next."Step6: Click "Startup Repair" at the "System Recovery Options" screen. The tool will automatically detect and fix startup errors. Your PC might restart more than once.
In first boot up your computer, your hard drive initializes by accessing its master boot record(MBR) but Windows 7 does not include native MBR backup capability. If you want create backup MBR then follow this blog-How to Backup MBR in Windows 7.

