I don't have time to dig up the threads now, but this happened to me several times in the past, on my old Mk2 and then on my current Mk2a. Interestingly enough, it's happened within the last two days, and it isn't showing any signs of going away.
Basically, if it's not the Hijack settings that Tony Fabris mentioned, then what's probably happened is the leaf switch inside the AC adaptor receptacle is acting up. The player uses a tiny little metal leaf switch in there to determine whether you're on home or car power. I personally think that's a design flaw, but I guess it was the most convenient mechanism they had to determine power source, and I guess they had no idea these switches would be so tempermental. Obviously it hasn't happened to everyone, but I've seen at least 4 or 5 others who've run across this at one time or another.
I don't care about fader/dimmer since I never really use them, but it's kinda frustrating to have only the one volume setting, and the worst part is that the Empeg doesn't power down when you turn the engine off. If this doesn't show signs of clearing up, I might be sending my Empeg on a little voyage. Unless someone here in the U.S. knows how to fix this problem.