Connect the ipad to itunes with the USB. When the ipad shows up. Click the device icon. On the summary page, scroll down and put a tick in the options section, allow this device to sync over wifi. Hit sync. When finished click on the eject icon next to your device, the little icon at the right of it. Then try to connect to wifi again.
If you have set up yOur iPad but it will not connect to your Wi-Fi network and go to the Internet, I think Coppertiger's suggestion will not help.
The first thing I might do to narrow down the problem is to go somewhere that you know has good Wi-Fi available. Your library, Starbucks, etc. Does the iPad connect there OK? If so you know the problem is in the router at home.
Here are some thoughts:
1. Check with the router manufacturer to see if there is a firmwarer update. If there is download it and install it. Then try to connect again.
2. You might change the routers security settings to something different. Maybe even turn off the need for a password to see if connection happens. If it does try a different security level.
3. What is the network name? If it is the same as the router manufacturer change it to something unique. It's amazing ow many Linksys Wi-Fi networks are out there. A nearby network with the same name could be causing problems.
4. Go to Settings> Wi-Fi > select your network name > then tap Forget this network. Then try to connect again.
5. Go to Settings > General > Reset > Reset all Networks. Then reboot your iPad. Press and hold the Home and Sleep buttons simultaneously ignoring the red slider until the Apple logo appears. Let go of the buttons and let the iPad restart. See if that fixes your problem.