I think Nanuq is on to something, but if you enable your Wireless router for DHCP from your ISP, then everytime you reboot or turn in off and on, it should get the new Gateway and DNS IP addresses from your ISP! Is your wirelless router connected directly to your cable/DSL modem? Or is there a Switch in between? If you have a switch in between, that could also be the culprit!
You should really do a reset and use the standard/default config after that and test without re-configuring it first, see if you could go out. Try and ping google.com and see if you get a reply back and an ip address (means your DNS is working!), if it does then you should be good to go. Now you could configure it the way you want it!
Good luck!