I had an old Hero vi that was notorious for giving me the 00 error. But never had that issue with my Hero 8 Alpha, which is similar enough to the normal 8. The cause of the 00 code can be a real pain to track down because it can be caused by several issues, but from what I remember reading, Ram is usually the prime suspect, but even your PSU, CPU or GPU can cause a 00 code! Your best bet might be to start by doing trial and error, and rule out one possible cause at a time.

Have you tried to loading optimized defaults in the UEFI and running everything at stock? Test one stick of ram at a time and see if you can make POST? Run the ram at stock non-xmp settings and see if you can make POST. Startup with no gpu installed? Try a spare PSU if you have one? Obviously it would be best to try the easier ones first, before getting into the more time consuming tests. My memory is a bit rusty on this particular issue, but lemme see if I can find you some more info that might help...

Not sure I understand your English here, can you re-word? You have to have at least the CPU and one mem stick in.

Have you swapped the power supply unit out for a new one?