Need help with Rotel 1067 receiver

I just got a receiver Rotel 1067, but could not have all 7 channels on. Only 5 channels works, fronts, center, subwoofer and sid surround. the 2 channels dont works are 2 center backs (surround back).

I only see all the lights for 7 channels are "ON" on the screen of receiver when I go to Multi Input.

And I could not go to MAIN MENU, even I did as the manual sai: OSD >>> ENTER... (I use remote when it is in AUD condition).

You guys have experienced in this pls help me. Many thanks!