Why is the flash drive not visible?

Question

linux

I plug the flash drive into the usb port. dmesg outputs

But fdisk doesn't see the media, sdb doesn't exist

What could be the problem?

Answer 1

I would first check the flash drive on another computer, because according to what you showed, the flash drive does not work: the controller is alive, but the memory is not. Windows for such flash drives should say "insert media into drive" when you try to access it.
You can try to reset the partition table, in case there is a jamb in it:
sudo dd if=/dev/zero of=/dev/sdb count=1 bs=512