As LtMatt says when things start going wrong and you've spend hrs trying to Diagnose and fix, an OS install is a bit of an ache in the underwear area but it usually sorts out a fair bit. Using a flashable USB and having games on a seperate drive actually it's quite quick.
This. I've reinstalled so many times this year. I can reinstall W8 and have everything back up and running in less than two hours these days. Games all go on my hard drive so i just need to reinstall OS, updated windows, mobo drivers and the rest.