itch.io

My best bet : 

1. Make sure your C drive has at least 10gigs free.
2. Run Antimalware / virus (I recommend Malwarebytes) 
3. Make a new session on your computer and start selectively transfering what you want to keep over it. Make sure to transfer all administrator rights to it including using your Microsoft login there instead by converting the previous one to a local account. 
4. If none of the above worked, try running a system repair. You'll have to Google how because it can vary from a machine to another.
5. Good luck !