In the first releases of KB947821, Microsoft warned customer on the information page about it that it would appear to be stuck: it still does that, but their warning seems to have disappeared.
I'm running it on my system at this very instant and it looks like it's stuck, but it isn't. Do not worry: just start it before you go to bed and forget it. If it still seems to be stuck when you wake up, then it really is stuck. You probably are going to want to run System Restore, to any time prior to when your daughter had the computer, since you don't know what happened when she was using it.
But before doing anything, even the KB947821, run a quick scan with whatever security program you are using. Then run checkdisk, but run the complete scan (it will be a 5 step process):
- Go to computer, right-click on your HDD and select Properties.
- Go to Tools, under "Error-checking" click "Check now", and in the little box that comes up, put a checkmark in both boxes, then reboot.
- It will run when it reboots, and will take hours to run, depending on how big your drive is.
- When it gets through, open an elevated command prompt (type
command into the Start menu search box, then right click on "Command prompt" when it comes up and select "Run as administrator").
- Type in
sfc /scannow, then hit Enter, and let that run. It may take a couple of hours.
Then and only then get the latest KB947821 (keep a copy on your desktop or on a removable hard drive; they just released a new version) and run it, as you have done. And run a complete system scan with your security program, then get Malwarebytes free version, download it, update it, and scan your system with it. That's your "second opinion" on security. I get a "third opinion" also on occasion, one of the online free scans, Trend Micro's House Call.
All of this will take a day. If your system isn't working at that point, you need to try System Restore. If that doesn't work, you will have to repair Windows one way or another, by doing a repair install or something of the sort. You may have to use the recovery console to get System Restore or even
sfc to work.