Which model of bontrager computer?

On the node 2.1 (i think all the nodes work the same), hold the lower right button to connect to the sensors and hold the two right buttons to pair the sensors (you only need to pair with the first set-up or a new battery, maybe).

Sensors transmit the data with a code that uniquely identifies the sensor. That way, the head unit can ignore sensors it hasn't been paired with (like sensors on the bikes of the people you are riding with). "Pairing" is the process by which the head unit determines which sensors it should listen to. You pair rarely.

The sensors are only transmitters (they don't get information from the computer; they don't care whether there's a computer listening at all).

When you are using the computer normally, it has to "connect" to the sensors. The nodes display the connected sensors at the top left.

My node works well but it sometimes drops the connection before riding (I get double dashes instead of the speed). Holding the lower right button fixes that. Note that you can stop the connection process by pressing a button once the indicators for the sensors you have stop flashing.

It seems that your issue is a connection issue (not pairing).

Try forcing a connect before you start riding. Spin the crank or wheel (either is enough) to wake-up the sensor and then put the head unit into connect mode. The crank/wheel does not have to be moving while connecting.