Win7 PC sometimes doesn't recognize undamaged audio CDs inserted into CD/DVD tray

[George]

I use a Windows 7 computer at work. It is a Dell Optiplex 3020 purchased in April, 2016. i5-4590 CPU @ 3.30 GHz, 8 GB RAM.

I borrow a lot of audiobooks on CD from the library. They all have multiple CDs - anywhere from three or four for thinner books up to 30+ for fat ones by Stephen King and other champions of verbosity. Most audiobooks average 8 to 12 CDs, I'd say.

At work, while working, I rip the CDs one after another to my C: drive so I can then drag and drop them to my mp3 player via USB. Usually this works fine. But sometimes, I have a day like this morning.

Arrived at work. Unlocked computer that I restarted before leaving work the night before.

Inserted audio CD into CD/DVD tray as always. Launched Windows Media Player to rip CDs as always. WMP said something like "insert disc". The usual list of tracks on the freshly-inserted CD did not appear, and WMP said something like "insert disc".

Browsing via Windows to My Computer also indicated the computer saw no CD in the tray.

I restarted. Same as before.

I restarted again. This time I was able to rip two CDs as usual, but then the computer wouldn't recognize the third CD. It might have been my imagination, but I thought the two CDs I was able to copy ripped more slowly than they usually do.

I restarted. CDs still not recognized.

Before I restart yet again or say to hell with it and do this at home instead, I thought I'd post here in case this sounds familiar to anyone.

Obvious things I've checked:

The CD/DVD tray goes in all the way and clicks shut as it should.
A green light blinks and I can hear the CD spinning as usual, whether or not Windows recognizes it
I've been around CDs long enough to recognize ones that are scratched, chipped, and otherwise physically damaged. These particular discs look excellent.

Any ideas?

Thanks.