Fixing Infinite Boot Loop
If the Startup Repair option fails, you will receive a message reading Windows cannot repair this computer automatically. At the bottom of the message, click View advanced options for system recovery and support to return to System Recovery Options, and instead click Command Prompt.
The black command line interface will open with X:\ selected by default; this is the Windows internal RAM disk that is used by System Repair. You will need to navigate to your Windows system drive, which will by default be on the C: drive.
To open this, type C: and press Enter. Type DIR and press Enter to check that you are in the right drive – the contents listed should include the Program Files, Users and Windows folders.
ou will then need to change directory. Enter CD \windows\system32\config and then DIR to check that the correct files and folders are listed:
· RegBack
· DEFAULT
· SAM
· SECURITY
· SOFTWARE
· SYSTEM
With access to the correct directory and the required folders present, enter MD mybackup to create a backup folder. Enter copy *.* mybackup to copy everything to this location, agreeing to the overwrite warnings when they appear.
The RegBack folder stores automatic Windows registry backups. To check if these can be used in restoring your system, enter CD RegBack and then DIR to view the contents. In the folder, you should have the following:
· DEFAULT, SAM and SECURITY files, each around 262,000 bytes
· SOFTWARE file, around 26,000,000 bytes
· SYSTEM file, around 9,900,000 bytes
Note that these figures are approximate, but recognise that if any of these files display a size of zero bytes then you will have to resort to another method of restoring Windows 7.
With your RegBack folder containing the data you need to restore Windows 7 and rescue it from the reboot loop, you will be able to copy the contents and use them to get the operating system back up and running again.
Begin by entering copy *.* .. – note the two trailing dots. These indicate that the contents should be pasted to the level above – the Config folder. Agree to all prompts concerning whether you want to overwrite files, and once the process has completed enter exit to close the command prompt.
On the System Recovery Options screen, click Restart to reboot your PC – if everything has gone as it should, Windows 7 should now start correctly!
From: http://www.makeuseof.com/tag/fix-windows-7-infinite-reboot-loop/