I jailbroke my ipad after I backed it up. Cydia wasn't installing anything so I decided to try to restore my backup and get cydia again, but after a backup restore my ipad is stuck on the apple logo.
Hold the home button and the sleep/wake button at the same time, for around 15 seconds. This should force your pad to reboot itself. Keep holding both, even after the screen goes black. When you see the apple logo appear, you can let go of both.
There is a tutorial in the hacking section that can help you get to your restored iPad. Then you can try the jailbreak again. You just follow the instructions. If you get an error while you are restoring your iPad you might have a firewall or your antivirus package is blocking the connection to apple. I ran into that before. Anyway the instructions are very easy to follow. Here's a link http://www.ipadforums.net/jailbreak...lsafe-method-restore-current-version-ios.html
If you have any trouble please post again.