All is fine the first 5 minutes, then image and sound gone

The durabrand dvd portable was fine. Now, i conect and the image and sound are perfect both, then after 2 to 6 minutes the light on the right becomes opaque and one icon in the screen appears, it is likea square with a line from the top right down to the left. Even if is conected to the power supply occurs the same. If the battery is not working suposse to function conected and on the other hand I tested with another ac adaptor and worked during 20 minutes and once again off. I want to buy a new battery and ac adaptor, and also a car adaptor, available in MIami. PLease help me, oh i lost mi manual, so i dont know the meaning of the icon and the change of the light intensity.