What they are referring to as a "ESC Main Board" is more than likely the main power board that the battery connects to.
Considering that board is much cheaper than the Lightbridge Controller, I would start there, order up a replacement, swap it in and if that doesn't work, then replace the Lightbridge Controller.
What you are describing could be either.
What was the failure mode? Did this thing land in water? Did it start out of the blue?
You have given ZERO background as to what happened and thus the ability to troubleshoot is limited.
Did you just buy it as a damaged aircraft? Did you crash it? Etc, Etc...