Try this, it happened to me while jailbreaking and this fixed it:
Hard Reset:
1) Power iPhone on.
2) Hold the Home and Sleep/Wake buttons for about 7 seconds, or until the screen turns black.
3) Your iPhone should reboot. If it doesn't don't worry, just hold the Sleep/Wake button for about 2 seconds.
Recovery Mode:
1) Turn iPhone off by holding down the Sleep/Wake Button for about 5 seconds or until the Slide to Power Off slider appears.
2) Slide Power Off slider. If iPhone is unresponsive, follow the Hard Reset instructions up to Step 3.
3) Open iTunes on your computer (Mac or PC).
4) Hold the Home Button down while you connect your iPhone to your computer via a USB cable.
5) iTunes should prompt you with a message saying an iPhone has been detected in Recovery Mode and that you must Restore it to before it can be used with iTunes.
6) Click Ok.
7) Click Restore a message should appear confirming that you want to Restore and Update.
8) Click Restore and Update. The restore has been initiated. Leave your iPhone connected until you iPhone reboots and syncs with iTunes.
David