Counterfeit copy of windows rid of message

Hi.
Help!
I have a windows 7 computer and everytime I turn it on and log in, first thing a message will pop saying "Your computer may be running a counterfeit copy of windows". Then later on more messages will pop up saying stuff like your copy of windows did not pass validation. Please help me. I need to know how to get rid of these messages. Also at the bottom of my screen it has a little message saying Windows 7, build 7600, this copy of windows is not genuine. Im not good at computers so please dont use complicated language :) Thanks