I found out why the Microsoft memory test was discontinued, it only tests up to 4 GB.
It gave a message that this was a limitation of that program, not the computer. So they knew.
I ran memtest86 for a while, it progressed through test 5 and part of 6 before I stopped it. No errors. I have 24 GB of ram.
The test was not exhaustive, but I will let it run overnight tonight.
So I have no memory problems, or no big ones so far.
No disk problems, I think.