Solved by reinstalling Windows 10.  MIDI works, audio works (I had lost audio, too, by updating the Realtek driver during troubleshooting.) Oddly, there is now almost a hundred files in the Realtek driver that weren't there before.  The drivers in my new synth haven't changed.  They didn't work before I reinstalled Windows 10, but now they do.
I have a brand new synth that is Windows 10 plug-and-play.  It is detected, installed, and the drivers loaded, but there is no MIDI signal coming from it into the USB port.  And I just discovered that none of my other MIDI devices are able to send MIDI to my Inspiron anymore.  They were all working perfectly a few months ago.  I have MIDI devices with manufacturer-supplied drivers and I have MIDI devices that are class compliant which use Windows generic drivers.  They still flash and blink.  They still have drivers that are "working properly" and which Windows finds no issues with.  But I'm getting nothing.  My DAW can't get MIDI signals at all.  I installed Protokol and Midiview, and neither one of those MIDI detectors sees any MIDI signal entering the computer through any channel. All I can think of that could have messed up MIDI is awhile back, long story short, I removed and reinstalled Realtek audio.   Has anyone else had USB MIDI connection issues?  If so, what did you do to solve it?  I've tried so many suggestions I've found on the internet.  My Inspiron is fully updated.  I'm dubious that replacing this laptop would solve anything, because I see so many other people with this problem. Thank you for any assistance you can give me.
USB MIDI no input