Hi John,
Managed to get into the mount again and re-tested the wiring and found that there was no resistance between the power plug and the main circuit board, so I then thought it may have been the board itself that was the issue.
Then, I tried Chris' idea of a replacement CAT5 cable. Suddenly, it worked! However, I was skeptical of the idea that replacing the CAT5 cable could fix it, so I decided to test things...
I turned the mount off and back on about 50 times by flicking the switch itself. On eight occasions, the mount failed to power on (i.e. it only turned on 42 times).
Then I left the switch in the ON position (once I had it actually on) and removed and replaced the power cable 50 times. The mount powered up all 50 times.
Hence, I conclude that there is an intermittent fault in the switch itself (or the wiring on the PCB).
Huzzah!
Thanks everyone for your help in identifying the issue. Now to figure out how to fix it...
