Try this - Reset the iPad by holding down on the Sleep and Home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons. (This is equivalent to rebooting your computer.) No data/files will be erased. http://support.apple.com/kb/ht1430
Some things to try first:
1. Turn Off your iPad. Then turn Off (disconnect power cord for 30 seconds or longer) the wireless router & then back On. Now boot your iPad. Hopefully it will see the WiFi.
2. Go to Settings>Wi-Fi and turn Off. Then while at Settings>Wi-Fi, turn back On and chose a Network.
3. Change the channel on your wireless router (Auto or Channel 6 is best). Instructions at http://macintoshhowto.com/advanced/how-to-get-a-good-range-on-your-wireless-netw ork.html
4. Go into your router security settings and change from WEP to WPA with AES.
5. Renew IP Address: (especially if you are drooping internet connection)
• Launch Settings app
• Tap on Wi-Fi
• Tap on the blue arrow of the Wi-Fi network that you connect to from the list
• In the window that opens, tap on the Renew Lease button
6. Potential Quick Fixes When Your iPad Won’t Connect to Your Wifi Network
Fix WiFi Issue for iOS 7
iOS 6 Wifi Problems/Fixes
Wi-Fi Fix for iOS 6
How To: Workaround iPad Wi-Fi Issues
Another Fix For iOS 6 WiFi Problems
Wifi Doesn't Connect After Waking From Sleep - Sometimes increasing screen brightness prevents the failure to reconnect after waking from sleep. According to Apple, “If brightness is at lowest level, increase it by moving the slider to the right and set auto brightness to off.”
Fix For iOS 6 WiFi Problems?
Did iOS 6 Screw Your Wi-Fi? Here’s How to Fix It
How To Fix Wi-Fi Connectivity Issue After Upgrading To iOS 6
iOS 6 iPad 3 wi-fi "connection fix" for netgear router
Apple's iOS 6 Wi-Fi problems
iPad: Issues connecting to Wi-Fi networks
How to Boost Your Wi-Fi Signal
Troubleshooting a Weak Wi-Fi Signal
How to Fix a Poor Wi-Fi Signal on Your iPad
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
WiFi Connecting/Troubleshooting http://www.apple.com/support/ipad/wifi/
How to Fix: My iPad Won't Connect to WiFi
iOS: Connecting to the Internet http://support.apple.com/kb/HT1695
iOS: Recommended settings for Wi-Fi routers and access points http://support.apple.com/kb/HT4199
How to Quickly Fix iPad 3 Wi-Fi Reception Problems
iPad Wi-Fi Problems: Comprehensive List of Fixes
Connect iPad to Wi-Fi (with troubleshooting info)
10 Ways to Boost Your Wireless Signal
Fix iPad Wifi Connection and Signal Issues http://www.youtube.com/watch?v=uwWtIG5jUxE
Fix Slow WiFi Issue https://discussions.apple.com/thread/2398063?start=60&tstart=0
How To Fix iPhone, iPad, iPod Touch Wi-Fi Connectivity Issue http://tinyurl.com/7nvxbmz
Unable to Connect After iOS Update - saw this solution on another post.
Note - When troubleshooting wifi connection problems, don't hold your iPad by hand. There have been a few reports that holding the iPad by hand, seems to attenuate the wifi signal.
Some Wi-Fi losses may stem from a problematic interaction between Wi-Fi and cellular data connections. Numerous users have found that turning off Cellular Data in Settings gets their Wi-Fi working again.
You may have many apps open which can possibly cause the slowdown and possibly the loss of wifi. In iOS 4-6 double tap your Home button & at the bottom of the screen you will see the icons of all open apps. Close those you are not using by pressing on an icon until all icons wiggle - then tap the minus sign. For iOS 7 users, there’s an easy way to see which apps are open in order to close them. By double-tapping the home button on your iPhone or iPad, the new multitasking feature in iOS 7 shows full page previews of all your open apps. Simply scroll horizontally to see all your apps, and close the apps with a simple flick towards the top of the screen.
Wi-Fi or Bluetooth settings grayed out or dim
If any of the above solutions work, please post back what solved your problem. It will help others with the same problem.
iOS: Troubleshooting stereo Bluetooth features
iOS: How to troubleshoot Bluetooth connections
iOS: Third-party Bluetooth accessories