I have mold in my bedroom, and i don't know why it is there or how to prevent it from coming back?

My room has 2 external walls, a window. The radiator is on. Behind lots of old videos i found white mold, there is also a damp patch on my ceiling. How do i prevent mold from growing? Should my window be open? I have moved my videos from there, will this help ventilate it and decrease the mold?