When you use My Computer to right-click a hard disk and press Format, the File system and Allocation unit size entries are blank, and you cannot format the drive.
This behavior will occur if the hard disk is larger than 32 GB AND the hard disk is removable or an external drive that is optimized for quick removal.
To workaround this behavior:
1. Right-click My Computer and press Manage.
2. Press Disk Management.
3. In the lower portion of the right-hand pane, right-click the disk you couldn't format, and press Properties.
4. Select the Policies tab.
5. Check Optimize for performance and press OK.
6. If prompted to restart, press Yes.