I put my My Nano-VNA into USB mode to try to connect to my Windows 10 machine by hitting JOG LEFT, i.e. holding the left button while turning it on. The screen flashes white. Now I can't get it out of that mode. JOG MIDDLE doesn't do anything, so my VNA is essentially useless. Advice?

According to the OwOComm User Guide UG1101, pressing the left button while switching on is a short-cut to entering DFU mode.
Looks like your unit is expecting you to reload the firmware. See the NanoVNA-QT Software on Page 29 of of the user guide mentioned above.

Here is a guess of what might fix it. Start up the NanoVNA-QT software. Look under the Device menu and see if your old firmware is there. If so, answer No to update.
I have never done this so it is all guesswork. Perhaps as you are in DFU mode it is time to load up the latest firmware?

Mike:

I think you've figured out the problem.  I put it into DFU mode intending to reload the firmware, which I couldn't manage to do.

I have the NanoVNQ-QT software running, but can't get it to talk with the NanoVNA because of problems installing the device driver. I'm running Windows 10 and thought I installed the driver, but Windows tells me that there is an "unrecognized" USB port and won't let me use it.  At least I think that's what's going on.

I may have to give up on Windows, but still would like to use the VNA, which was working fine before I put it in DFU mode.  The must be some way to get it out of DFU mode directly?

thanks,

david.

If all fails, open it up and remove the battery for a short while. Worse case you end up with a unit without firmware and that puts you back where you are right now.