Also ancient copies of restore points.
First thing to do is just run their own tool, Disk Cleanup. They do at least dump some of the most egregious crap with it. Including emptying the Recycle Bin, which is often home to all sorts of useless crap when I sit down to get paid and grit my teeth at a Winderz box.
And nobody asked if you’d done that, which is either a sign they all trust you, or they forgot “first things first”... haha.
(If you come back and tell us you got half the drive back by emptying the Recycle Bin, no... never mind. Do not tell me that if you did, because I would start to wonder if you really should fly airplanes. Hahahaha.)
Standard family computer crap list, off the top of my head:
Run the Microsoft Disk Cleaner.
Uninstall every freaking application they say they don’t use.
Uninstall system features they don’t use.
Clean up and reset the defaults to something sane for Restore Points.
Figure out if Winderz did something stupid with their swap or hibernation space. Slap it around if that stuff is set wrong.
Clean out their Download directory. Teach them to move things they want to keep elsewhere and empty the whole dir regularly. Unless they’re horribly disorganized and beyond hope of ever creating folders or their own filing scheme for anything, in which case just sigh and delete anything that’s easily downloaded again.
Search for large files by file size. After finding sixteen copies of one illlegally downloaded movie, suggest to them that one copy is plenty and said filing system might be a good idea.
Check that they have some sort of antivirus and malware software and make sure it’s been updating.
Check that Windows Update has been working and that it’s set to continue working.
Usually by now I’ve managed to get them back huge amounts of space, the machine is working decently, and I lost interest long ago. Around the second item.
Go find something to drink, preferably alcoholic if not driving, and hope for the further encroachment or tablets that are completely locked down, for their sake. They really shouldn’t have a computer.
I’ve had so many Christmases ruined now by “Oh can you look at the computer?” that I’m used to it... oh sure... I’ll be happy to work for eight hours downstairs in your corner basement office while the rest of the family is up here enjoying each other’s company... sounds effing awesome! LOL.