Sorry to hear you are having difficulty here with shutting down. I had a similar issue with my dell inspiron e1505 once on Ubuntu 7.04 (feisty).
Would you mind telling us a bit more. The hardware you are using, what version of mint you are using, and maybe any changes you made recently?
The more information ya give, the easier it will be for some guru to help ya.
The greatest glory in living lies not in never falling, but in rising every time we fall.