Al,if the PS or 24vdc is getting pulled down the screen does not come up.I have that fault on a machine with a 6T.Every year at so at switch on nothing happens,no screen nothing.It`s a short on the machine side,proved by unplugging cables from the connections board.I have never yet found the fault despite spending days at it.It`s a large lathe and digging about in the wiring seems to move whatever is shorting and it powers up