Turn off the ACCUGUIDE and switch to lightbar - if that works then the NAV II is the problem. Reload firmware on the nav and it might work again, or you need to get the NAV II repaired 

I had the same problem earlier this year when one of the batteries in my 310 failed.  It messed up a bunch of controllers and the NAV II, luckily reloading firmware fixed my issues.

Good luck