How to protect my application??

I've application on certain pc & I want only that pc to execute it,so I've thought about getting a unique identifier (e.g. processor id ) using c# .

Problems :
I know that solution isn't usable because if the processor on that pc is changed so the application won't work any more .

Initially, how can I make that kind of protection by getting a unique id.

If any one has a better idea plz tell me about it.

The problem with all such schemes is that anyone with half a mind to hack it can find out where you do
if ( key == magic ) doProgram();

And turn it into
if ( key != magic ) doProgram();
to enable the code to run on every machine EXCEPT yours.