I'm having the exact same problem with my system as well, except I did the hardware bypass on the system almost a year ago. Mine does the exact same things, resets itself until sometimes it will actually boot up but then I had to enter my anti-theft password, and no Nav signal.
I figured maybe one of the connections came loose in the back of the stereo so yesterday I rewired the whole stereo. And now the stereo still does the same thing, except now when it comes to the anti-theft screen and asks me to enter my password the entire keyboard area is greyed out and now I cannot enter my passwo