HI Wompoo,
I just read your post and the reply to it. Here are my thoughts on this as well.
I know that you have 3 older computers, 2 x 64-bit desktops and 1 x 32-bit laptop. Is this happening on all computers or just one, if just one, which one? Is this with your new USB 64gb stick or all USB sticks?
Assuming the drive is recognized by your system, there are usually 2 simple methods for mounting or unmounting a removable drive like a USB stick. One is using the "Device Notifier" system tray panel icon, and the other is using your File Manager. Of course, you can use a partition manager or "Disks", and there are console terminal commands as well. There are also removable drive options in the Linux Mint systems to automatically mount removable devices or not to; Tip: if you are making bootable USB sticks, it is best to turn off these automount options until you are finished.
"Device Notifier": When you first plug in a USB stick, the "Device Notifier" should automatically show a pop-up window where you can click actions or the "triangle" on the right of that drive (USB stick or drive) to mount it (make available) or to unmount it (eject it, safe to remove). If the USB device was already connected, then you can just click the "Device Notifier" to bring its pop-window to do this. If the "triangle" in the "Device Notifier" next to the USB drive is pointing up, then the drive is already mounted and available to your system, if the "triangle" is pointing down, then the drive is not mounted and safe to remove, or click the "triangle" to mount the drive and make it available.
"File Manager": If you bring up your file manager like "KDE's Dolphin", you can click the drive on the left side (may have to scroll up or down to see it) to mount it, or right-click it to click safely remove it (unmount it).
If you are having issues with one particular USB port, try another USB port...
Hope this helps ...
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