Then you need to do as requested.
1) Connect to iTunes on the computer you usually Sync with and Restore...
http://support.apple.com/kb/HT1414
2) If necessary Place the Device into Recovery mode...
http://support.apple.com/kb/HT1808
Note on Recovery Mode.
You may need to try this More than Once... Be sure to Follow ALL the Steps...
Once you have Recovered your Device...
Re-Sync your Content or Restore from the most recent Backup...
Restore from Backup > http://support.apple.com/kb/ht1766