umm...Unless you have a ground wire loose or disconnected on the back of the dash, there isn't anything else it could be BUT the power supply...I've had mine go out in the past(year and a half ago)...Trust me on this one...
I know it's expensive to fix, but short of picking up another used dig dash from someone upgrading to a GNX style dash, there isn't any other way to fix it...The problem with getting one from someone that is upgrading, is that it probably won't last very long either...The way that John Spina explained it to me, is that the heat from the sun and the age of the components, that he is seeing more and more of the power supplies going bad lately...
Sorry for the bad news...