Heatbed does not heat up (no replies)

I bought a Flsun printer cube and it came with the Makerbase MKS Gen L V1.0 board. Here is a link to the product.
After only a couple of prints I have encountered a problem, the heatbed no longer heats up.

This is what happens:
When the heatbed it's power wires are plugged in the LED indicating power is being routed does NOT turn on.
If I unplug the wires then the same LED indicator DOES turn on.
If I plug the wires of the heatbed directly into the power supply it does heat up.
The temperature is being correctly read though through the sensor.
And yes the wires are in the correct +/- terminals.

What is going on and how do I fix this problem?