The line from your modem to your router ... does it plug into the yellow ("internet") port on the router? If so, you have probably created 2 different networks that can't talk to each other. If this is the case, try putting your router in "bridge mode" (pg 33 of manual http://downloads.linksys.com/downloads/userguide/1224701614608/MAN_WRT1900AC_8820-01897_RevA00_EN_FR-CA_Comprehensive.pdf).
Alternatively, you can move the plug from the modem from the yellow port and into a blue port instead of the yellow. Make sure you turn off DHCP (pg 27).
After doing either of these, devices connected to the router will need to get new IP addresses. Restarting them is the easiest way to renew the IP address.