If you get a virus on your SD card, your SD card may be hidden. Now, you can try using CMD (command prompt) to fix this issue.
Click Start button.
Search command or cmd.
Right-click or tap the Command Prompt search result, and choose Run as administrator.
Type diskpart and press Enter.
Type attrib -h -r -s /s /d drive letter:\*.*( for example, attrib -h -r -s /s /d k:\*.* )and press Enter.
attrib -h -r -s s d k
Finally, type Exit.