- Insert the USB drive and open up Disk Utility.
- Click on the actual drive name, not the partition/s.
- Click Erase.
- Select whatever you want the name to be in the name field.
- Select MS-DOS (FAT) or ExFAT depending on the Win file system you want.
- Select Master Boot Record for the scheme.
- Click Erase.
- Once done, unmount and try it on your windows machine. Should work.