Just tried to start one of the pc's and all I am getting is the main power light (red) and the disc activity light (green) flashing on and off. Nothing is booting up.
Is this indicative of a power unit failure or if not where should I start on the diagnostics.

I'd have to assume that your PSU is fine (for now) Your PC is accessing its drive and would seem therefore to be OK. I'd tend towards thinking your Display side is failing in some way shape or form.