Chkdsk error issue help needed

Hi guys,
I need some help from you who have wide knowledge in computer troubleshooting. Last week, I ran the disk de-fragmenter utility of my PC to reorganize the noncontiguous files that I have in my hard drives. While it was running, I received the check disk error and it instructed me to run chkdsk/f.
When I initiated the disk check in the command prompt, it informed me that the hard drive which my laptop is using was used by another volume. I repeated the steps carefully but the de-fragmenter kept on showing me the same error.
Please give me any recommendation on how to solve this problem and it will be highly appreciated. Thanks.
