diagnosing a heated bed
Switch the hot end and the heater bed wires on the board. See if there is a difference. (Note that it will not reach a thermal limit when plugged in this way! So don't leave it on too long!)
After that, if you see that your heat increases with the hot end's wires and the hot end being set on in software then you know the issue is likely with the board. At which point try updating / reflashing the board.
Alternatively, you can try a second board and see if it makes a difference.
If the bed does not heat up even using the heater cartridge connectors, then your heated build plate likely needs to be replaced. Or the wire needs to be replaced.
If you are running Ramps or a board that uses 2 hot end outputs you can likely reprogram it to use hot end heater 2 as the new output for your heated bed.