we all faces a problem like the invisible memory cards on mobile or pc. So try to short out this problem by the following steps:
1.first go to the the control pannel and select the view as small icons.
2.select the folder option in it and select view and click on show hidden files and apply and ok.
3.now open the cmd in admintrator mode and play the following cmds.
4. Type “DISK PART” and press ok.
5.Type “list volume” and press Enter.
6.Now recognise the disk u want to format i prefer to rocognise be it size.Type “select volume ” and press Enter where is for the volume u focussed.
7.Now enter this command.format /q /x : and press Enter.
Note: Don't forget to replace the letter "" with your drive letter.
8.And if there is still problem then try to go through boot menu by inserting the memory card.
9.open the cmd in boot and format by the same cmd it will also ignore the privacy if added to the memory card.
Thank you.