I would suggest steps 1, 3, and 5 of the iPhone Troubleshooting Assistant found here http://www.apple.com/support/iphone/assistant/phone/#section_1. If you get to step 3, close all the apps. Here is step 1 to get you started:
To restart iPhone, first turn iPhone off by pressing and holding the Sleep/Wake button until a red slider appears. Slide your finger across the slider and iPhone will turn off after a few moments.
Next, turn iPhone on by pressing and holding the Sleep/Wake button until the Apple logo appears.
Is iPhone not responding? To reset iPhone, press and hold the Sleep/Wake button and the Home button at the same time for at least 10 seconds, until the Apple logo appears.
If your device does not turn on or displays a red battery icon, try recharging next.
If that does not work then I would troubleshoot iTunes for 3rd party plugins in safe mode with this article:
iTunes: Troubleshooting issues with third-party iTunes plug-ins
And if the issue still persists in safe mode, I would recommend recreating your iTunes library.
iTunes: How to re-create your iTunes library and playlists