My Pioneer P7900UB goes dead during use (appears to be at random), but when the ignition is turned off it beeps and the face folds down like normal (but will not do anything when the eject button is pressed before turning the ignition off), and when the ignition is turned on again it works fine. I have been told this is likely to be a "protect" mode although I don't know much more about it, other than bad speaker connections can cause it. I have taken out the stereo and there's nothing obvious shorting or anything.

Is there anything with my car's electrical system that may be causing the stereo to do this?

TIA.

Can you reset the h/u? There might be a small push button either on the face or when your remove it. Sounds like a dodgy connection. I would have a closer look at the wiring on the plug.