iPad: Basic troubleshooting
http://support.apple.com/kb/TS3274
Update and restore alert messages on iPhone, iPad, and iPod touch
http://www.buybuyla.com/tech/view/012953a0d412000e.shtml
iOS: Resolving update and restore alert messages
http://support.apple.com/kb/TS1275
iPad: Unable to update or restore
http://support.apple.com/kb/ht4097
iTunes: Specific update-and-restore error messages and advanced troubleshooting
http://support.apple.com/kb/TS3694
iPad not appearing in iTunes
http://www.apple.com/support/ipad/assistant/itunes/
iOS: Device not recognized in iTunes for Mac OS X
http://support.apple.com/kb/TS1591
iOS: Device not recognized in iTunes for Windows
http://support.apple.com/kb/TS1538
iTunes for Windows: Device Sync Tests
http://support.apple.com/kb/HT4235
IOS: Syncing with iTunes
http://support.apple.com/kb/HT1386
Apple - Support - iPad - Syncing
http://www.apple.com/support/ipad/syncing/
iTunes 10.5 and later: Troubleshooting iTunes Wi-Fi Syncing
http://support.apple.com/kb/ts4062
Cheers, Tom 😉