1) If it only ever restarted in XBMC (which I don't think is the case from your description), I'd try
wiping XBMC's data first.
2) Try a factory reset via the
Android Settings/Backup & Restore function.
3) Try a
cache wipe and factory reset (I need to check sometime, it could be the factory wipe involves a cache wipe anyway) via the iMX6's recovery menu (don't forget that instead of the OK button, you'll need to use the Return (Go Back) button on your remote to select entries in this menu).
4) Assuming you've not already upgraded to the
Android iMX6 May 2014 firmware, see whether flashing to that helps.
In all cases, don't forget to run the
DroidBOX Wizard add-on afterwards, and if you've tried steps 2, 3 or 4, waiting 20 minutes after you reach the Android launcher's homescreen (for apps to have time to reinstall).
If steps 2 or 3 don't automatically reinstall the apps (possible with very old firmwares) after twenty or so minutes, skip to step 4.
Step 1 will result in all of XBMC's data being wiped away, so backup or make a note of extra add-ons you've manually installed, configuration changes you've made etc etc
