Restoring Registry - System Will Not Boot

Was wondering if someone can help me fix a big mistake I made?
I clicked on a registry backup file that did not belong to the computer the backup file was located on.
I did not follow the rule I always stress – Think before you click.
Both systems are running Windows XP Professional.
Now I am not able to start the computer, it keeps looping back to the Safe Mode screen.
I have tried selecting the different Safe Mode selections, no help. I also tried booting into the Last working configuration.
I do have a registry backup file for this system, just don't know how execute it since I am not able to boot into windows. I also have System Restore points set.
I hope that I have supplied enough information for someone to help or direct me to where I can find it.
Thanks
Steve
I clicked on a registry backup file that did not belong to the computer the backup file was located on.
I did not follow the rule I always stress – Think before you click.
Both systems are running Windows XP Professional.
Now I am not able to start the computer, it keeps looping back to the Safe Mode screen.
I have tried selecting the different Safe Mode selections, no help. I also tried booting into the Last working configuration.
I do have a registry backup file for this system, just don't know how execute it since I am not able to boot into windows. I also have System Restore points set.
I hope that I have supplied enough information for someone to help or direct me to where I can find it.
Thanks
Steve

Steve, that's a bit of a mess if I'm honest mate and something I personally wouldn't want to have on my hands !!
However, help may be at hand using this KB from Microsoft - give it a read through and hopefully you may be some way towards regaining access to your system ...
http://support.microsoft.com/kb/307545
However, help may be at hand using this KB from Microsoft - give it a read through and hopefully you may be some way towards regaining access to your system ...
http://support.microsoft.com/kb/307545

That's a good call Marko, useing the recovery console to enter new registry commands is the way to repair it . The only other way to make sure it is 100% fixed is to format and reinstall the OS,,and that is really not a desired option!!!! 
