Hard drive space missing...

[alexDimitro]

Hello, I am having this really weird issue with one of my disk partitions. D is an individual drive of 1 TB, as seen in the image it says I have about 30 GB left free space. However when i click inside, highlight everything including the hidden files, it only calculates to about 500 GB. So I have round about 400 GB of disk space that is there, but somehow taken and I dont know what is taking it. Any ideas ? 

[Electronics Wizardy]

How many files are there? Lots of little files will use more space than the files actually need due to the cluster size.

[TheBean]

screenshot the disk management settings

[alexDimitro]

Re there are about 20K files on that partition, which is not that lot. I use the drive to store my current working projects (I am a video editor) 

Re Saksham this is the image of disk managament I dont see any issues here. 

[homeap5]

It may be a bug in display correct free space. You can use MiniTool Partition Wizard, shrink partition just a little (by 1MB for example) and then run chkdsk. You can also try just checkdisk without shrinking first.