Modem keeps dropping connection

I'm on a Macbook Pro hardwired to the modem which is a Motorola Surfboard. I was originally running wireless with my linksys wrt54g but then the internet wouldn't work at all on my mac because the modem would drop the connection as soon as I tried to access the internet. I hooked straight into the modem and now it sometimes works. Now it just randomly drops the connection and then I have to power cycle the modem, and sometimes I have to it do it a couple times before it works. But I play live on my xbox 360 hooked up straight to the modem and I have no problems at all with it. I don't think it's my mac or the router, I'm pretty sure it's a problem with the modem. Help?