Power cycle the modem by removing its power cord for 10 seconds, then plug it back in. If you have a telephony modem (EMTA), simply press and hold the Reset button until the device reboots, pulling the power cord does nothing on these EMTAs since they have internal batteries and don't lose power. Some models reset best if you remove the coax as well.
After the modem is back up and talking to Comcast, follow your router's setup instructions to connect to the modem and configure the router.
That said, I have heard complaints from several sources about the Linksys E1200 as being a subpar device. Linksys usually makes good stuff, but I would always avoid bottom of the pile models like this. If you have an issue, update the firmware to the latest version and if things still don't work, step up to a better model, like the E2500 or E3200.