Back up the Registry

The registry is critical for health of the system, sometimes even a small tweak, may corrupt windows and avoid from logging in. So it is always recommended to back up the Registry before applying any of your changes.
To take the back up of the registry open registry editor from start > Run, type Regedit and press enter.



In Registry editor select the highest key from left pane of 'My Computer' and then from top level menu in registry editor select File > Export, give the location where you want to store the
back-up, and its done with backup of complete registry.
On can also backup particular key, to do that same way select the key from left pane and click on File > export.

To apply the backup again you can simply double click the backup file or clcik on File > import from Registry editor.

Users using Windows ME and higher can also create system restore points, to save all the current settings of windows (including regitry). To do this navigate to start > program > Accessories > System Tools > System Restore, and select 'create a restore point'. To revert to this point later, you have to just select the point again to restore.