You have to confirm the shore power is getting to the converter. Assuming other 120v things work. The converter is on one of the 120v breakers--check that.
If the converter is plugged onto a receptacle, unplug it and plug it in to a known to be live receptacle, extension cord if required.
If it is hardwired, not a plug in (such as a Parallax 7xxx) your 120v is behind the metal panel covering the breakers. Take that off and find the black wire going up from the converter to its breaker. The white wire goes to the neutral buss. Check those wires for 120v. Another way to check that breaker is move the converter's black wire over to another breaker where you are for sure getting 120v.
If you are getting 120v to the converter itself, and no DC output, there is a 120v glass fuse on the converter's board where the 120v come in. You can jump that to see if it is blown.
If no joy, you can post the converter model and get recommended replacements. (The "PD guys" will say get a PD and I will say get a PowerMax, but that's only if you get that far )