How much was it overcloaked? Did your computer actually become invisible or just hard to see?
Ok, ok, I'll be serious.
Sometimes it just happens that the symptoms of an unstable overclock only appear when using certain applications, that's probably the case here, even if it's only one game most likely hardware instability is to blame. I would just try stock clocks and see if that fixes it; if not, then it's most likely an issue with the game itself.