Mamiya RB67 ProS wont trigger or advance

Start by making sure the dark slide is removed, the camera will not fire with it in place. The next step is to check the rotating back to make sure it is locked in either the vertical or horizontal position. Without film in the magazine, the multi-exp lever on the back must be set to show the red dot under the advance lever. You can check the camera without the back by removing the rotating back using the latch on the bottom of the camera