Wifi log in > won't let me log in

Change security on modem to WPA/WPA2-PSK (TKIP/AES). Apple products seem to demand the highest levels when made so try this. If this is already in place, change your wi-fi name and password (really!) I always run into Apple wi-fi issues. If all else fails, do a hard reset on your modem (hold red reset button in for 30 seconds or use GUI to get into advances modem settings/admin/restore factory defaults.
Also if your using a mac/iphone, choose channel 1 or 11 on the router, dont let it auto choose for you.