I've only seen this happen twice (on two different Windows installs) since that last major 8.1 update (update 3?), but PC Settings will stop working, and I don't know why. Starting it gives a "This app can't open" bar with "There's a problem with PC settings. Refreshing your PC might help fix it.". I reinstalled Windows a few weeks ago, and PC settings was working fine up until recently. I don't recall doing anything significant aside from running Windows Update a few days ago, and it picked up a few recent updates. I haven't tried it yet this time; but sfc /scannow didn't help before. Anyone have any ideas?