how can i repair my d2?
i change reg file :S need to reinstall d2?

Yea, you'll need to reinstall unless you have the file backed-up in another folder.

It depends what you changed.

The only reason to mess with the registry is when changing your default channel that you enter.

If you made a mistake doing that then I can most likely assist you with getting back to the default.

Other than that I recommend you reinstall DII.