I posted this in the ""Problematic HD-DVDs" thread, but it seems to actually be a problem with the new version of MakeMKV. I had to revert to v1.9.10 to get it working again.
There seems to be something wrong with 1.10.1 in regards to HD-DVD (and/or the 360 HD-DVD drive). I was trying to make an mkv of a new HD-DVD I'd bought and it couldn't get past the initial scan after clicking the big "Open HD-DVD disc" button.
So I inserted a disc I'd used recently and it did the same, so I knew there was a problem. But the last time I made an mkv was on w7 I think, whereas I'm now on w10 (w10 home, ver. 1511, os build: 10586.545). So thought it may just be my HD-DVD drive (not exactly a new bit of hardware). I even went to the trouble of using VMware Player to create a w7 virtual machine to test it (same results).
But then I came on the forum and read the post by 820am in the ""Problematic HD-DVDs" thread, so I found an older version in my download folder (v1.9.10) and tried that.
I swapped to a free USB 2.0 slot on my motherboard (the USB 3.0 port was disconnecting itself), but after that I've had no problems. I managed to make an mkv of the new disc, it's extras and another previously used disc just to be sure.