you need to enter the security code into the radio to turn it back on. athe code can be obtained from the dealer through the vin#.

the stereo has power when turned off for the memory of the preset stations, etc.

once power is removed from the stereo (like a thief removes it) requires the code to turn it back on.

as far as the engine problem goes, i do not know how that relates to the stereo.

good luck,

dan