Good day there, I'd like to tell you that I've been in a situation like this before. My memory card was always functional with my PC, but one day it stopped working and disappeared on it. In my experience, this problem happens due to all sorts of reasons, for example, poor connection, SD card reader or adapter corruption, outdated SD card driver, or SD card file system corruption. You need different solutions to deal with this trouble according to the reasons, while the first one you should try is to check the connection.
You can grab a soft cotton to clean your SD card gently, re-plug it into your PC, and then see if it can be detected by your computer.
If not, try another SD card reader to connect the memory device and your computer. If a new SD card reader makes your SD card detected, then it's the fault of your SD card reader. Read this article to fix your SD card reader that stops working: SD Card Reader Not Working, How to Fix?
If your SD card still fails to show up on your computer, I guess it has some faults. I am sorry to tell you that you should drop this problematic SD card and try a new one for your future storage work. Meanwhile, data recovery is impossible because your SD card cannot show up on your computer.
Hope you good luck!