From memory te power for the pc and monitor are 110v in the cabinet.  Most pc power supplies will let you change from 240-110 with a red switch

+1 I'm guessing you haven't switched to 110v, its a sliding switch on the pc power supply. But remember once you do this, you need to change it back whenever you plug it externally on a bench etc as you have mentioned as you will be pumping 240v into a 110v setup and that will cause problems.

Neon could be a few problems from the tube, transformer or chip on the power driver pcb. Check out a few threads on here that addresses neon isssues