Sounds like your MOST bus is down, you need to get it hooked up and have codes read, until then you are just shooting in the dark.....It could literally be anything.

To get to the hud, the ip needs to be removed.

pin 5 is power (30G2 switched from bdc)
pin 11 is gnd, straight to chassis (not switched.)

pin 1 is MOST in
pin 2 is MOST out

MOST pin 1 will be BLINKING red if the MOST is operational, if it is not blinking and solid red, or OFF the MOST is down. Hope this helps