When you say that the "Windows partition" is taking up 300 GB, do you mean that C:\Windows is 300 GB or do you mean that you have other partitions (e.g., D:, E:, etc.) on the hard drive?
- If the latter, what is in those partitions and what size are they? A laptop is likely to have a partition on the hard drive that contains the computer manufacturer's recovery software, but I would be surprised if such a partition was 200 GB in size.
- If the former, 300 GB is way too big for the C:\Windows directory.
Download TreeSize Free: https://www.jam-software.com/treesize_free
Run it "as administrator" (if the shortcut doesn't say "Administrator," then right-click the shortcut and select "Run as administrator")
What command did you use to run your scan?
100 GB for Program Files and Program Files (x86) sounds like you have far too many application programs installed, but TreeSize Free will help you narrow down exactly what is taking up the space.
Check out C:\Windows\Temp. If this folder is full of files with names following the pattern "cab_XXXX_X", generally 100 MB each, you're suffering from a known bug. See this article for an explanation and a method of fixing it: https://www.computerworld.com/article/3112358/windows-7-log-file-compression-bug-can-fill-up-your-hard-drive.html
If you don't have the "cab file bug" and running TreeSize doesn't suggest to you what you need to delete, post the names of the 5 or 10 folders (or files) that take up the most space.