My device was fully charged and has been unresponsive for 24 hours now.

Do a

Reset: Hold down the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. Note: You will not lose any data

2 more basic troubleshoot steps:

Restore from backup

Restore as new

http://support.apple.com/kb/HT1414

If no joy, make an appointment with your local Apple Store for evaluation.