Zero returned by the RegisterHotKey confirmes that CTRL+C has been registered by some other process. Only that thread can unregister CTRL+C.

Probably check the list of running processes in your Task Manager, may be you find some strange guys. Try to kill them manually. Of course it's not completely safe, there's no other choice.

So far I'm not aware how to obtain a process handle by hot key value. Will check, it's actually quite interesting... :)