I really need help with this!!!!?

Ok so I just got the wireless adapter for m Xbox and a gold membership... I connected to everything except Xbox live. It said the MTU was supposed to be 1364. Mine is 1452. I have a wireless belkin N+ router and I was able to change the MTU to 1364. Now when I did that the modem light and the Internet light started flashing orange. It wouldn't let me connect to anything (e.g iPod, laptop ect). What do I do because I spent a lot of money on it.