Generally speaking, if Windows 7 won't start, it is likely this tool will help. It can perform tasks such as:
- replace missing boot files
- update the master boot record
- update the boot sector
- repair the boot configuration database (BCD)
- repair driver issues
- remove invalid operating system files added by malware
- remove faulty services
- Boot from the Windows 7 DVD
- Click Repair your computer.
- Click Use recovery tools that can help fix problems starting Windows.
- Click Startup Repair.
You can manually perform some of the same repair tasks by using the Command Prompt option and the Bootrec.exe tool. You can use Bootrec.exe to:
- Fix the MBR without losing the partition table (bootrec.exe /FixMbr)
- Fix the boot sector to load bootmgr (bootrec.exe /FixBoot)
- Scan disks for Windows installations (bootrec.exe /ScanOs)
- Add all Windows installations to the BCD (bootrec.exe /RebuildBCD)
You can perform a System Restore from inside Windows 7. Or, if the system is too unstable to perform a System Restore from inside Windows 7, you can boot from the Windows 7 installation DVD and perform a System Restore from the same menu as a Startup Repair.