We just moved a few days ago, so we moved from our old ISP to our new one. On our old ISP, I connected using the DIR-615. On our new ISP, I still use the DIR-615, but a different modem. Now I cant connect to the internet unless I plug it directly to my computer.
your modem can be set to bridge mode and then the WAN side of your router would be configred with the login information for your ISP.
best way to do this is call your ISP and request their help in that matter. Reason some ISP use a login protocol that not all routers support. They should be able to change the modem for you remotely and provide you with the necessary login info.
there should also be a setting in the WAN setup to 'Stay Connected' at all times