Ok, routers and iPads sometimes get at logger heads. Let's try something a bit more thorough.
Go to the Wi-Fi Settings on your iPad, select your network, and tell it to forget it. For good measure, turn the iPad off by holding down the power button until you get the power off slider, then slide it off.
Now restart your router. Leave the router off for at least a minute, to make sure RAM gets clear.
Start the router.
When it is up and running, start the iPad, go to the Wi-Fi settings and join the network.
That's about as complete a reset of the relationship between the iPad and router as I can manage without fiddling with the router itself.
Luck.