@Asteroid Lady: I think you mean 16 GB RAM? This is of course large enough. If it would have been 2 GB it could be unresponsive I guess.

The render PREVIEW settings could matter because of hardware shadings. But with 16 GB RAM there can't be a memory problem.

So the problem must be somewhere else.

You followed SSGBryan's recommendation which would have been my first answer to solve this problem too. Then you answered that "they are working now". So far...

"But:

I have this M4-based character that I've been working on a long time, kind of in the background while doing various side projects. He's my favorite, and I've put a lot of time and care into him. Because he was started before I ran that file to fix M4, his morphs are still in the long sloppy list, and I still can't load the body morphs from Morphus or this one other set, and I think he needs them. I had been morphing his body one part at a time, because the one morph set would load the morphs for the individual parts but not the full body ones, and they weren't smooth, I had to be careful to match up all the seams and then sometimes when I posed him they would split, so I would like to just start over with that set. I don't want everything I've done so far to go to waste."

I have the feeling your saved morphs in the file do not correspondent with the paths in your file. Do you have Poser File Editor? With that you could analyse the path file to the morphs. For example, for M4 base morphs from DAZ:

readScript ":Runtime:Libraries:!DAZ:Michael 4:Deltas:InjDeltas.M4BaseAll.pz2"

You can find that also with the simple editor in your Windows version. Can you open your saved file and find the line that directs to the Morphus morphs? If so look if the path is correct and also if they are really in that folder.

Also to look for:

according to the DAZ product page Morphus morphs require the product 'Michael 4 Morphs ++'. You probably have it, otherwise you couldn't have worked with it before...

And is it possible that you saved your file with "external binary morph targets" (under Misc in General Preferences)? Then there must be also a *.pmd file. If so look for it.