Hi Enterprisingguy!!
So, you're saying that the pc only using up 20GB of data, and it shows that 77GB of precious space has been used, am I right?
Before I guess something, can I know how many partition drive his computer have? Is it only one, or more than that? And how did he summarize that only 20GB of data has been used by his computer?
Just to clarify everything, ask him to go inside each partition and see how many free space left form the total, so the data used should be equal to difference between both.
Space used = Total space - Free Space
And then, ask him to select all the folder inside the partition, then right click on any folders after select, and click Properties. By now, he should get the total space consumed by all the files. If the space consumed is same like the space used, then there is nothing to worry about. But, in case the size is not matching, there is a problem.
You might want to try click on menu under any folder windows,
Tools,
Folder Options. Then, you should be on
General tab, click on
View tab. Choose the "
Show hidden files" and remove checkmark from "
Hide protected operating system folders and files" and then click
OK.
By now, you should be able to see all the hidden folders and files. Ask him what is the size of page file (should be the file named pagefile.sys), and also the size of "
System Volume Information". If total of this size sums up to the space used size, then it is correct
You can try to delete all the files inside folder System Volume Information,but make sure you didn't delete the folder itself. You can use a software Unlocker
(Download Unlocker) for this purpose because this folder is protected by system.
Make sure you have created the system restore point before perfoming any action in case there is anything goes wrong
You might also found some unknown folder or files which takes out of some large space. Maybe this can be deleted safely, but I hardly recommend you to post the screenshot and details of files/folder here first before going ahead and delete them
Hope this helps