The laws of thermodynamics and their relation to perpetual motion machines?

Using the laws of thermodynamics, explain why a perpetual motion machine cannot exist.



I know why it can't, energy has to be lost in some form, but I'm not entirely sure how to relate that back to the three laws.

Any help would be greatly appreciated.

Thanks.The laws of thermodynamics and their relation to perpetual motion machines?first law, energy is conserved, that's all I think.