My xbox 360 slim won't connect to the internet anymore! Whats wrong?

I used to be able to connect to my router with my xbox 360 slim and i brought it to a friends house and connected to his router and now my xbox won't connect to my router anymore and the wireless internet works on my laptop and when i plug in an ethernet cable, and it can find my router but won't conect to it. I also tried putting in a static IP adress intead of it atomaticaly doing it but it still doesn't work. How do i fix it?