Did you put the motion sensor closer to see if it even shows up in the activity monitor? If they don't trigger at all when close by then you probably have a couple of bad sensors.
You must me using the cm15 if you have AHP. Using the 2 tm751's is not a good idea because they step on each others signals (their not polite)
Have you tried without the use of the tm751's?
Also motion sensors will put out the code that you input +1 (example: sensor is a1 so the sensor will send a1 and a2 for dusk and dawn signals)
A simple example of a cam setup would be: cam1 c1, cam2 c2, cam3 c3, cam4 c4, cam5 c5, cam6 c6. motion sensor b1 for cam1, b3 for cam2, b5 for cam3, b7 for cam4, b9 for cam5, b11 for cam6.
Also make sure that all the cameras and receivers are using the same frequency (switch under rubber plug, all to A or all to B, C, D) reminder that this is just the frequency switch and has nothing to do with the house and unit code on the power supplies.
A good way to check the motion sensors is to take them close to the computer and cm15 and open the activity monitor, while watching the activity monitor wave your hand over the sensor or move it and see if the red led flashes, then look in your activity monitor to see if the cm15 is receiving its signal.
You might want to tell us exactly what equipment you are using and what the unit and house codes are for each piece of equipment and what you are trying to do because like I said some of your equipment doesn't like to play well with others.