You might also try putting the phone into DFU mode and try to restore it. If you are continuously receiving the same restore error then a DFU restore may still be able to rectify the issue because it removes and replaces both the software and firmware.
To put the phone into DFU mode:
1. Make sure the phone is connected to the computer
2. Hold down the sleep/wake button and home button at the same time for 8 seconds
3. Let go of the sleep/wake button and keep holding down the home button
4. If you are successful, a dialog box will pop up in iTunes stating that iTunes has detected an iPod/iPhone in recovery mode.
5. Click OK, then click the restore button in iTunes.
Hopefully after that, the iPhone will be up and running so you can sync your content back.