Seen this too (with AVG installed)
Got a PC in this vicious circle just now; you can't roll back as that fails, you can't use system restore as there aren't any restore points; Windows helpfully tells you to reset your PC but the reset option isn't available!
Best you can do is boot to a "different OS", i.e. back to your botched non-desktop. Most stuff won't run - stuff as basic as Explorer for example. services.msc does, control panel doesn't; disabling the AVG related services doesn't help at all.
Looks like the only way out for this is a reinstall from scratch. I could probably count on the fingers of one hand the number of times I needed to do that for Windows 7 (and previous) - you can virtually always fix it when things go wrong. With 8 onwards, if the various basic "system restore" s fail, you've had it. Utter rubbish.
I think the person who owns this PC may get it back running Linux (with her consent of course)- she only needs it for basic word processing and email, and at least once she's got used to which buttons to click for Libreoffice and Thunderbird they will stay put. With Windows 10, who knows what the next unwanted update is going to add/remove/destroy?