First, there is no 'Mountain Sno[w] Leopard'... There is Mountain Lion (10.8) , or Snow Leopard (10.7), so it's worth checking what version you have.
Secondly, there's no way anyone here can 'check out your Mac' - we can't see it or access it. All we can do is give you some pointers as to things to check. The first thing is what do you mean by 'does not work'?
Do you get an error message? nothing at all? a blank page? or it starts to run but stops unexpectedly?
There are many, many defintions of 'not work'ing, and knowing your symptoms is essential in diagnosing the problem.