Looks like I spoke too soon about there being 5 machines. The new machine (Anakin) is working fine but Yoda has given up the ghost.
Yoda has been running the CPU fan flat out for the last 3 weeks or so. I checked the BIOS which displays the core temps and it wasn't reading the fan speed at all, so I decided to open it up. I thought it might be clogged with dust and fluff but there was nothing to see. Now it won't power up at all. It just beeps constantly. It looks like I will have to make a call tomorrow to see just how good the ACER 3 year on-site really is.
Rang ACER tech support and got position 42 in the queue, so hung up. Yoda seems to be back working so I suspect its the intruder detection, even through its disabled in the BIOS. It still runs hot but i'll leave it for the time being.