Viewsonic VX 800 blinking/flashing green LED light

A strange problem is occuring with a Viewsonic VX 800 monitor. Whenever it is switched on the green LED flashes constantly (every 0.5 seconds) and nothing appears on screen. But, after a prolonged period, the blinking will slow to once every 7 seconds. Perhaps not even after a long period. It is attached to an apple mac and when it reboots the screen sometimes comes on. Quite random. I guess what I'm trying to say is that I've not fully tested the situations out.

I found a few mentions of stuff but not very helpful. I guess because the screens are quite old.

Here I found a service manual but it's not very helpful