Try rebooting your router. Turn it off for a couple minutes, then turn it back on.
While it is off, go into you iPad settings, General > Reset, and reset all network settings.
When the router comes back online you will need to go to the network settings on the iPad and rejoin your network, so make sure you remember the password and security settings you chose before.
Reseting the router often works all by itself, so if you don't want to fool with the rest you can give that a try first.