Ah - I see where you are going. Sorry - I obviously have not made myself clear. The installed graphics card is an nvidia GTX 750. The manjaro livedvd will not boot with that card installed, that's why I tried the GT440. That did not work either, so I now know the problem is not card-specific. Hope that is clear. I will see if I can edit the post title. Also relevant:
This PC currently runs several linux distros (all deb based). They all boot fine with both those nvidia cards.
The dvd player will boot just fine if I try several previous DVD-burned iso's that I have still around the place. So it is not a problem with the dvd drive.
I have just downloaded Chakra and the iso of that boots fine when burned to a dvd - both free and non-free options. I noted that the first boot entry using the free option gave the same Nouveau MMIO fault as the Manjaro boot attempt but still booted OK, so it doesn't look relevant.
The dvd I made of Manjaro boots and installs just fine on another similar PC but will not even boot on this PC.
See my problem?
Thanks for the tip about inserting code in a post