Look at iOS Troubleshooting Wi-Fi networks and connections http://support.apple.com/kb/TS1398
iPad: Issues connecting to Wi-Fi networks http://support.apple.com/kb/ts3304
iOS: Recommended settings for Wi-Fi routers and access points http://support.apple.com/kb/HT4199
Additional things to try.
Try this first. Turn Off your iPad. Then turn Off (disconnect power cord) the wireless router & then back On. Now boot your iPad. Hopefully it will see the WiFi.
Go to Settings>Wi-Fi and turn Off. Then while at Settings>Wi-Fi, turn back On and chose a Network.
Change the channel on your wireless router. Instructions at http://macintoshhowto.com/advanced/how-to-get-a-good-range-on-your-wireless-netw ork.html
Another thing to try - Go into your router security settings and change from WEP to WPA with AES.
How to Quickly Fix iPad 3 Wi-Fi Reception Problems
If none of the above suggestions work, look at this link.
iPad Wi-Fi Problems: Comprehensive List of Fixes
Fix iPad Wifi Connection and Signal Issues http://www.youtube.com/watch?v=uwWtIG5jUxE
If any of the above solutions work, please post back what solved your problem. It will help others with the same problem.
As I live in an apartment a few of my neighbours have open wifi I can connect to these using my phone 4 and my iPhone 4s but the iPad will not connect.
But unfortunately i do not have access to a router of that type
Also to add when I am trying to put wifi password in I have full signal for the network and sometimes (1 in a 100)it will connect but once I move 6 feet away it says I have full signal still but nothing just stuck lodging
Have a look at the article mentioned by Texas Mac Man,
http://appletoolbox.com/2010/04/ipad-wi-fi-problems-comprehensive-list-of-fixes/ and try the brightness thing, maybe it works. If not, you'll have to get it serviced or looked at in an Apple Store.