messed up permissions windows 10

Hello all, Dave here. I have done something that I have done before, with windows 7 on down. I had a laptop that had a broken power port, and the battery went dead. I ordered a new power socket. While I was waiting for parts, the owner wanted files off of it. I removed hard drive, hooked it up to my pc, which is windows 10 also. To access the files I had to take ownership of the drive. this seems to be a big issue with windows 10, that I could easily fix up afterwards with win 7 pro, xp ect. I tried searching threads, but didn't find one.
The laptop is pretty messed up now. slow, over 15 mins. to get to desktop, some programs won't open at all. access denied messages intermittently. I also found no restore points, so that option is not possible. I attempted to take ownership of C: where the operating system is installed, with TakeOwnershipEx . Confusing software, that did not produce any noticeable changes.
I wanted to do a factory reset, but some software has lost installation media. The one program that is stopping me is, what looks like a retail version of QuickBooks. It's over 1000.00$ to replace.
Is there any way out of this situation? I have a bootable usb with recent windows 10 on it from Microsoft website. Pulling what's left of my hair out. Thank you in advance for any advice, Dave

Welcome to the forum. We need to know what ownership you tried to do doing it on c could kill it as a lot of folders need to be owned by system. You may be able to do a system refresh keeping files and apps it may not work sepending what you have done