The RAMBo board has red LEDs to indicate that power is being sent to the various outputs ie. hot end, PEEK fan, heated bed, etc. These LEDs are below each of the associated outputs. When power is being called for, you should see the LED turn on for that output. If you manually heat the hot end you should see two RED LEDs light up on the RAMBo, one below Heat-0 (Hot End) and one below Heat-1 (PEEK FAN). Check and verify that these LEDs are lighting up when you manually set the heat. Do the same for the heated bed. (the red LED below Heat-2 Bed should light up)
If the LED for the output (you have identified as not working) is turning on it means that the RAMBo is calling for heat and you need to identify why the element(s) is/are not heating. The next step would be to check the wire connections at the particular terminals (input/output) for loose connections and tighten up all the screw terminals. For HE280 hotends, this could also indicate that you have a fault with your thermal fuse in the heatsink of the hotend and will need to replace it. If you have a multimeter you can verify this.
If the above is not occurring you need to find out why the RAMBo is not call calling for heat. The next step would be to clear the EEPROM and reinstall the firmware in case something has been changed that shouldn't have been.
NOTE: Before clearing the EEPROM, it is a good idea to access the EEPROM via MatterControl (or other host software) and record the values for your Diagonal Rod Length, Z Max Length, and Horizontal Radius so that you do not have to re-calibrate after the re-install of firmware.
Here is a guide for clearing and installing EEPROM: Installing Firmware