Vector 750 Watt Maxx SST Inverter

I have had the above inverter for a number of years. Always worked fine camping with small items like electric coffee pot. Had it in storage for a few years. Took it out and tried it, but nothing works. Turned on power switch, but neither the red or green light comes on. Hooked up a small electric light to the outlet, but doesn't work.
Battery connections all clean and solid
Cable connections to inverter all clean and solid
3 automotive type fuses inside inverter all OK
Terminals on back of power switch seem OK. Used continuity tester, no continuity with switch off, continuity with switch on.
Can't figure out how something could have gone bad just sitting in safe, dry storage for a few years, but what do I know?
Any hints on what a non-electrician can try next?