For boot or startup issues, use the built-in recovery environment: Repair System Startup for Windows 7 [Tutorial]

If you are specifically trying to fix registry keys or issues preventing software from being installed or removed, Microsoft provides a direct Program Install and Uninstall Troubleshooter that still supports Windows 7. 3. Essential Windows 7 Updates (Manual Fixes)

System Update Readiness Tool : Scans for and repairs corruption in the Windows servicing store. 4. Advanced System Repair (F8 Menu)