Likely your registry is hosed. Have you run any registry repair or cleaner on the system? That would do it. Try a system restore. If that doesn't work, save all you important data and reinstall the OS.
I have had the same thing happen. The control panel was not accessible due to a registry repair progam I ran. This happened twice. On the first occasion, I was able to do a system restore and recovery access to my Control panel. The second time, I had to reinstall the OS.
This looks like a bigger system problem. You may need to reinstall. If it was just the control panel not coming up you could reconfigure the software licensing service like here http://annoyances-resolved.blogspot.com/2009/11/vista-c... but it seems to me it is a bigger system problem. Tell us what happened.