Most motherboards have both a mic slot and line-in, I'll assume you know which one is which. That said, is it possible that the mic wires were broken inside the cable when it was yanked?
I don't have two mic jacks hooked up to my pc so I don't know how they affect one another (if at all). I would perhaps suggest unplugging the broken jack from the motherboard (if you post your motherboard model I can help you with that).
Alternatively, I would try and find another mic you can test in your system, or even find another system to test your mic. It's hard to know what damage has been caused, but it's unlikely (from what I know) that one damaged mic jack on the front would affect the rear one.
