Which Windows OS?
Registry editing. As you have found, it is full of difficulties and dangers.
Try a System Restore back to some date before you tampered with the registry. If that fails in Normal mode, try Safe Mode where you have "Last known good configuration".
There is no guarantee this will succeed. So if you don't have backups already you may want to backup all your personal files before trying this.
Recently I had a message on my computer warning me of low disk space, I tried moving the installation path from the os to the local disk. I went into the registry editor changed the name and now i get the error. I CAN'T DOWNLOAD ANYTHING NEW!!!!!!!!! I want to download double twist but I can't. I can't back up my computer at this point so restoration is impossible. Yes, I have tried to go back to the registry but it gives me "C:\Windows\regedit.exe Make sure you typed the name correctly... Help!