First port of call is to reset the router by pressing an unfolded paper clip or the point of a biro into the reset hole on the back next to the power plug , do this carefully while the router is plugged in and turned on . Connect the router to your PC with an ethernet cable and access the set up pages as you did before when you first set it up ( type 192.168.0.1 into the address bar on your browser and then press enter .
The login in for the router is " admin " and the password is " password " without the quotation marks , go through the various wizards for finding your internet connection and for setting up some security ( WPA is preferable )
When your internet connection has been found and some security set up , detach the ethernet cable and try connecting wirelessly again .
See how you get on from there !!