I have suddenly lost the Wi-Fi on my iPad. Me and my friend have a Wi-Fi account with AT&T and his iPad Wi-Fi is working just fine. Why not mine?
You will need to restore your iPad. Hold down the top and bottom buttons till the screen goes black and you see the Apple symbol. Then follow the instructions on this page http://support.apple.com/kb/ht1808 to restore your iOS. I think once you do this and re-sync your ipad a lot of your problems (that you have posted about on here today) will be resolved.
Restoring is far too drastic for this issue until all other avenues are reasonably explored. if resetting network settings (under settings) or a simple reset doesn't fix it (power off by holding sown sleep button and holding it again to turn back on), looking into wifi network issues would be the next step. Restoring is not guaranteed to work, and YOU WILL LOSE/WIPE EVERYTHING.