Replying to Macbook and its wireless connection problems.

I have looked on google and tried a couple thing, i zapped my pram or whatever that is and i did'nt help.

My wireless used to be very good and i could go anywhere in my house and be perfectly fine, but now it will die in my room and i have to sit in the computer room so i can sit 6ft from the modem.
It sucks, i know its not the modem because my sisters laptop didnt have problems.

What can i do, im not sure if i want to take it to the apple store because i have a pirated fcp.