@smilelikemiles Sorry, I had a busy day today and wasn't online until just recently. I should be on tomorrow morning, around 10 am PST and for a couple hours after that.
The guide I linked has screenshots of almost everything you'd see during a repair install, and I couldn't explain the process better than it does. An ISO is an install medium, sort of like a disc installer without the disc. The guide has a link for creating one, which Microsoft makes extremely easy: you go to a website and click a few things, then wait.
It's possible that one or more of your computer's Windows updates were interrupted, resulting in some kind of corruption that hasn't been fixed. That's just speculation on my part, and there are plenty of other possibilities too, for example malware or an overzealus cleaner app. The important thing is that the errors in your dxdiag are real and should be addressed.
As for the Task Manager, I still think a repair install is necessary, so there's not much point in checking startup tasks beforehand unless you're curious. 48 background processes isn't high in and of itself, especially since a single application or driver can have several entries. The Startup tab will be more illuminating.