Are you using a range extender? If so, your provider may not allow certain extenders. CenturyLink just turn off my internet if I hook up my netgear WN3000. All I get is the strong signal and no internet connection.
On another blog, I asked if anyone else had there modems firmware updated without their permission.
I think they did mine so they could turn off the modem if my netgear was working, but I bought another modem thinking that it was my modem, because it worked for 13 years, before I got to check for the update, they won't let me hook it back up to find out if they might have broke the law. So check your firmware and make sure they didn't do it to you. Mine was done about the 1st on May.