Monitor showing no picture
First thing is to ensure you are using the correct power supply which should be either a 13.5V 1100mA OR a 12V 1000mA power supply (this is written on the back of the power adaptor unit, directly after the word "output").
If that is correct then please try and alter the brightness and contrast on the monitor using the dials located on the back of the monitor.
Please check whether you are able to get any sound out of the cameras, and also try swapping the camera ports over and re-connecting all the plugs ensuring they are fully plugged in to the unit and making a good connection.
Please ensure that the yellow RCA plug is going to a yellow RCA input, and the red RCA plug is going to the white RCA input.
Please make certain that you connect the cameras only to the lower sets of RCA plugs that are yellow and white and NOT to the upper set, which is a group of yellow, white, and red as those are for output only and will not yield a picture.