Hey Thomas,
I think the first check should always be the supply circuit and then the power cable. You would use a multimeter to check them, by setting it to 250 V AC and inserting the probes first into your wall socket, and then in the cable end of your C13 plug.
Next would be opening the box and checking the internal crimp contact that go to the switch / button, and to the fuses, also by measuring with a multimeter.
I would check if you have this issue:
Then if there is AC voltage everwhere, I would check the DC output of the internal Meanwell LRS-350 power supply, with the multimeter set to 50 V DC.