Windows 7 fails to start in any mode. What to do?

My recommendation would be to back up and reinstall. This is a last resort, but a quicker fix than troubleshooting if you need the machine.

NOTE: Although this article makes several references to Windows Vista, it still applies to Windows 7

Startup Repair. Startup Repair is a Windows recovery tool that can fix certain problems, such as missing or damaged system files, that might prevent Windows from starting. Startup Repair is located on the System Recovery Options menu, which is on the Windows Vista installation disc. If your computer has preinstalled recovery options, it might also be stored on your computer's hard disk. For more information, see Startup Repair: frequently asked questions and What are the system recovery options in Windows Vista? If your computer does not include Startup Repair, your computer manufacturer might have customized or replaced the tool. Check the information that came with your computer or go to the manufacturer's website.

Change restart settings in safe mode. If your computer is stuck in a loop where Windows fails, attempts to restart, and then fails again repeatedly, restart your computer in safe mode and select the Disable automatic restart on system failure checkbox. For more information, see Advanced startup options (including safe mode).

Reinstall. If no other options have solved the problem, and you are sure that your computer's hardware is functioning normally, you might need to reinstall Windows. A custom (clean) installation of Windows will permanently delete all of the files on your computer and reinstall Windows, so only use this option if all other recovery options have been unsuccessful. After the installation, you will need to reinstall your programs and restore your files from backup copies. For more information, see Installing and reinstalling Windows‌‌.

Also check this out