A USB What? (eg) Flash Drive, USB HDD, SD Card Reader, etc?
I assume you mean a USB Flash drive?
Go to Search and type diskmgmt.msc, right click the diskmgmt results and Run As Administrator in the Disk Management window do you see your Flash Drive there? Does it say the File system is Unallocated Space or does it say the Disk # (eg) Disk1, Disk2 etc is Uninitialized?
USB Flash drives are Volatile and known to fail because of their portability.

 

On the disk manager it says this

Gyazo - b7c7fcad1251e72f96131bf106586cdb.png

 

If your USB Flash drive is plugged in when you go to Disk Management, it would show up as another drive on a separate line (eg) Disk # (Disk1, Disk2) on the left panel. If it is not showing, as the picture attached shows, then try it in another computer. If it doesn't show on that computer in Disk Management, then it has failed and needs to be replaced.

 

if you had the drive plugged in when you took the screen shot, you need to replace the drive.