I’ve seen this scenario a couple of times now on Windows 10 machines. I’m not 100% sure what has caused it each time as the machines were brought to me in this state, but it appears to be a corruption to the registry.
The scenario – most programs fail to open. Everything from office to task manager fail to start – windows just asks you which app you want to use to open the .exe file. You can’t run a command prompt, and you can’t edit the registry. Strangely Microsoft Edge does appear to run?!
To fix, you need to start by rebooting into Safe Mode with Command Prompt. This choice is important – the same happens in Safe Mode, so you need to be sure to select the one with the automatic command prompt.
Now run regedit and locate
Change default key value to exefile.
change Default ket to “%1” %*
I also ran a check disk and an sfc /scannow (which came back clear) though I don’t think these were necessary.