Apps / Software :: Start Screen Apps Not Working Including Store

About three days ago, all new style apps stopped working. I click on the tile, get a deep blue screen, and nothing else. On the left side of the screen, I can see the app as if it is working (just the name of the app, not content), so I can close the window and get back to desktop. The same applies to the STORE app. The only tiles that work, are the links to desktop applications, which open correctly on the desktop. The fault also affects all windows system apps. For example if I search on the start screen for "windows update", I can access "Windows update" as it just opens a window on the desktop, but if I click on "Windows update settings" nothing happens. The same is true with all windows system apps that open in the new start screen system.

I've uninstalled two Microsoft updates that were installed over the past three days, no change. I uninstalled AVAST, no change, so I reinstalled it! I tried restoring the system, but found that I had only one restore, and that was corrupted. Very strange. Without access to many windows system apps, the computer is really limited. The desktop seems to be working OK. I can't refresh the PC, as firstly it is a system app that runs from the start screen, and secondly because I upgraded from win 8 to 8.1 online, this can't be done anyway, as I don't have a disc. I'm really trying to avoid reinstalling windows 8!

(Pavilion dv6, i7 processor, 6GB ram, originally win7, then I upgraded to win 8 and now 8.1. I've been running 8.1 for some months without problems, just occasionally on start-up from sleep, I get "error in non-cached memory" BSOD, and the system restarts.)