Hi, I am Dave, I will help you with this.
1
Right click your Start Button and open Disk Management.
Expand the bottom pane of that window so all drives are visible in that pane, please provide a screenshot of that window.
2
Open the Settings App, then go to System - Storage - Advanced Storage Settings.
In the 'Where new content is saved' section are all settings set to use that new drive?
3
Click the link below to download a small free utility named Treesize.
https://www.jam-software.com/treesize_free
Very Important - to run TreeSize, you must right click its icon and choose Run as Administrator.
Please provide a screenshot of your C drive in that TreeSize utility, so I can see your hard drive and work out where that space is being used and if there is an underlying problem.
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