Why can't I connect to xbox live?

OK. I moved in december, so i couldnt have my xbox hardwired to the router anymore, so i got a wireless receiver ( a mad catz ). Anyways, it worked fine for a few months, then it stopped connecting because the MTU setting was too low, so I checked it and it wasnt too low so I reset my router and everything was fine for a couple weeks when it wouldnt connect again. I tried resetting it and restoring everything again and it wouldnt work. I even bought a new router (the other one was old) and still it wouldnt connect. I tried everything. I called xbox support and they said it was the internet providers fault. I called the internet provider and they said it wasnt them, it was the router, so i looked up everything on how to connect to xbox live with the router and still nothing would work. I literally tried everything. I dont know whats wrong someone please help. My internet for my laptops still works fine though. HELP