I had this problem a couple of months ago and we had a thread here about it. Last time, new RAM fixed it.
I try to boot our VKM3 Centurion 6 mill and it hangs in different places or just reboots as it tries to load the final conversational screen.
I replaced the RAM again with no luck. The power supply checks out ok.
It flashes a message about "No Video Input" and then reboots right as it is about to finish the boot-up process most of the time.
This machine has led a pampered life in a clean area and has only accrued 145 hours in it's 4 years here.