First off you should think if you changed anything recently, like driver updates, updated your computer or Operating System? That could give BIG clues to whats the problem.
What type of OS are you using?(ie,xp,vista,7) is it 32bit(86x) or 64bit(64x)?
When I updated my pc to a new 64bit win 7 model, my old wireless g would not work due to compatibility issues(no driver update).
Always try first:
1. unplug all power to router and modem for 30 sec(differs with model)and pc if connected through gateway.
2. Connect router first(wait for full boot-up) then connect modem(wait for full boot-up)then re-boot router while modem is still green(this allows the router and modem to communicate and prepares to open ports. Sometimes the order needs to be reversed to create a comm link.
3. Next thing would be to make sure its the router and not your internet connection(modem) itself. Plug directly into the modem (bypass the router) and make sure you get internet.
4. Last but not least, check to see if you can access your router(everything connected during this test), open up a browser and type your provider I.P.for your router into the browser bar at the top of the page,( ie. 192.168.1.1) different providers are a little different, if it allows you to access your router then it is communicating, and may be being blocked by firewall preferences or closed ports.
Any questions concerning this, feel free to email me
[email protected]