Firstly I would check that the file system isn't corrupt as you could run into all sorts of issues. Please try using chkdsk (Windows built in disk checking tool) to check:

• Open a command prompt as administrator
• Type chkdsk C: /F and press Enter
• It may well inform you that it cannot lock the volume and requires a scheduled check at boot time, in which case enter Y and press Enter. You'll need the server/VM to be rebooted for the check to go ahead and obviously there will be some down-time.

If this doesn't work you could try the procedure below. I would recommend getting a full backup done beforehand though

• Open a command prompt as administrator
• Type diskpart and press Enter. A new command-prompt should appear.
• At the DISKPART> prompt, type list volume and press Enter. This will show all the volumes on the system
• Type select volume # (where # is the number of the relevant volume) and press Enter
• Type extend filesystem and and press Enter

This should adjust the filesystem to use all available capacity in the volume and is based on several articles on the web, including this KB article.

Firstly I would check that the file system isn't corrupt as you could run into all sorts of issues. Please try using chkdsk (Windows built in disk checking tool) to check:

• Open a command prompt as administrator
• Type chkdsk C: /F and press Enter
• It may well inform you that it cannot lock the volume and requires a scheduled check at boot time, in which case enter Y and press Enter. You'll need the server/VM to be rebooted for the check to go ahead and obviously there will be some down-time.

If this doesn't work you could try the procedure below. I would recommend getting a full backup done beforehand though

• Open a command prompt as administrator
• Type diskpart and press Enter. A new command-prompt should appear.
• At the DISKPART> prompt, type list volume and press Enter. This will show all the volumes on the system
• Type select volume # (where # is the number of the relevant volume) and press Enter
• Type extend filesystem and and press Enter

This should adjust the filesystem to use all available capacity in the volume and is based on several articles on the web, including this KB article.

If that still doesn't work, you could try repeating the above but use extend instead of extend filesystem as this will extend the volume itself if there is unallocated space on the disk. But I don't think that is the issue.