First I put only a single stick in and booted fine.
Then another stick and booted fine.
Then a third stick and got this message:'
'Free Magic is broken at 0x8255a360: 0x2c3c2808
That was followed on the way to powering off by a 'disk boot failure' message.
and I had to power down.
Removed that third stick again and rebooted.
Got one of those muticoloured pixellated screens. Though they're not really pixel blocks, bigger than that, maybe a 1/4" long each one. Reminds me of years ago we used to get that sort of thing on those old graphics cards.
Went and tried again and this time was able to add all four sticks in one at a time and it booted into Linux Mint each time.
Thought I was fine. Then it locked up. Won't respond to keyboard or mouse. Nothing.