I keep getting disconnected from Xbox Live

Happens about 5 minutes or so after everytime I sign in.  At first I thought it was a problem with my router so I plugged the ethernet cord straight into my modem.  About 5 minutes later I was disconnected again.  I  called my internet provider and they ran a test told me that they didn't detect a problem on their end, but detected a problem when the connection tried to run through MSN. I tried to see if netflix still worked but I still get disconnected about 5 minutes or so into the movie or show I try to watch.  Still skeptical I took that same ethernet cord and plugged it into the back of my PS3 ran netflix watched a whole movie and played games with no interruption.  I'm not sure what the problem would be, I have had the same modem for years and have had no issues before.  Even had no problems playing on live the night before.  I've ran the connection test and it connects just fine,  like I said before, the problem doesn't happen until about 5 minutes after signing in.