There are some simple things to test:
- Verify the AC outlet has power.
- In rare occurances the OBC power down mode, drive cart for 5 minutes and retry
Some common things go wrong that require some voltmeter skills:
- Batteries are severely under charged, I believe the pack must have around 38 volts for the charger to start.
- The relay in the charger goes, just replaced one last year on my Par Car
- The on board computer has issues.
- OBC fuse is blown
If you are a DIY'er with a voltmeter I can send some pointers....