1. Power phone down, pull battery.
2. Remove any new apps installed (since you have already eliminated this, skip)
3. If you have an SD card, remove it and try phone without it. (sometimes a corrupt file on sd card can cause issues)
4. Clear the data for TouchWiz Home: Menu>System Settings>Application Manager>TW>Clear data.
5. Clear the Cache: Power phone off>Hold volume up + Home + Power> Wipe Cache Partition>Reboot.
6. As a last resort, you can do a factory reset (or your carrier probably will do this when you take it in) ***Make sure to backup, you will lose data.