Registry errors may cause many problems, including the inability to boot the operating system on your computer. If you're reasonably certain that your registry errors are causing your computer to be unable to boot, you might try putting your hard drive in another computer as a secondary or "slave" drive and then trying to edit the registry. This can be done by loading the registry hive files from the secondary drive from within the Registry Editor program running on the primary drive.
Click the "Start" button and type "regedit" into the Search field, then click the "Registry Editor" program.
Click "HKEY_LOCAL_MACHINE" in the left pane of the Registry Editor window.
Click the "File" menu and choose "Load Hive."
Browse to the secondary hard drive's "windows\system32\config" directory from the "Load Hive" dialogue box.
Click to select the "System" or "Software" file (no file suffixes) to open the respective registry hives. Type a temporary name and click "Open" to open the hive.
Click the "File" menu and choose "Unload Hive" when you have finished editing the registry hive on the secondary drive.