Examine the DC power connector. Make sure that it's securely in place and plugged into a working electrical socket. If the HMI light is not working at all and the power indicator fails to brighten, the power connector is the most likely suspect. If the HMI light comes on and then quickly dims, make sure that the power supply or batteries are fully charged and working.
Remove the fuse from the lamp if your light is not receiving power yet the DC power connector and the power supply are working. Replace it with a new fuse. Each brand of HMI lights is different; if you do not know how to replace the fuse, refer to the manufacturer's manual.
Examine the condition of the barn door's safety chain and pin if the doors are loose. Tighten the screws if necessary.
Remove the bulb from the lamp if the HMI light is receiving proper power but not turning on. Examine the bulb for signs that it has burned out. The presence of black powder bulges or blisters are signs of a burnout.
Turn the power to the light off it your lamp begins making a buzzing sound. Wait for the bulb to cool before checking that it is properly placed in the socket and not loose. Expel a deep breath into the front of the light to place humidity into the light. Step away from the light and power it back on.