Well...first of all check if the router is connected to ur modem correctly. The cable from modem should connect to the back of the router which has a label called "internet or WAN". Try to unplug everything and plug it back again. Check if all the lights on the modem are proper. Then try the installation again...if it still doesn't work...try the manual method...i.e.
Click on Start...Go to RUN...Type in "CMD"......press enter.
U'll get a black command prompt window...go ahead and type in "ipconfig" and press enter....u'll get some info there. Go ahead and note down the DEFAULT GATEWAY...(its a set of number...something like 192.168.1.1).
Close all the windows...and open ur browser...e.g...Internet explorer...and type in the number u get for Default gateway ...on the address bar...and press enter...It should take u to the router homepage or it may ask u for an id or password....try to type in admin in the userid or password field...or if u have already given an administrative userid and password...go ahead and type that.
Now u'll have the Linksys home page. On the Left Hand side...top of the screen ...u'll find a option called "INTERNET CONNECTION TYPE"....next to that u'll have a drop down menu...go ahead and click on that and select....the option which u want...Most of the ISP require u to select the option called PPPoE. If so select that...and type in the userid and password provided by ur ISP....Then scroll down and click on save settings or apply...
Now...once on the Right hand side top of the screen... u'll have a tab called status...click on that...and see what u have next to connection status or under PPPoE. If it says connected then ur connected and good to go.
P.s. Make sure that u have the modem in bridge mode...
GOOD LUCK>