Well, on Windows you can try running a CHKDSK command for the drive. If that doesn’t resolve the problem you can use Windows DISK MANAGEMENT to delete the partition, reallocate the partition and reformat it, exFAT preferably. There is also the possibility of using Windows’ DISKPART utility to do the same thing. Unfortunately both options will delete all your files. Hopefully you have backups of them.
I’m not a Mac person so I don’t know what your options are on it.
