A display apparatus and a method. The display apparatus may include a display, an interface configured to be connected with an output terminal of a source device, a main processor configured to control an operation of the display apparatus and a sub-processor configured to identify whether the output terminal of the source device is connected with the interface. The main processor may identify whether the source device is turned on if the display apparatus is in a first state, and the sub-processor may identify whether the source device is turned on if the display apparatus is in a second state. The main processor may control the display to display a UI based on one or more of whether the interface is connected to the output terminal of the source device and whether the source device is turned on.