Hi again
Thanks for letting us know the extra details: very helpful.
The trouble with the Windows 10 Start Menu and Cortana going haywire has cropped up a few times in the early months of this six months of Windows 10. There are several ways to try to fix it - we've already tried System Restore. Some of the other fixes are: 1) creating a new user profile (temporarily, and hoping for an eventual patch from Microsoft to fix things - so you can return to the original user profile), 2) A method that checks for system file corruptions & attempts to repair them, using tools briefly called SFC and DISM, 3) a method that re-installs all the Windows apps (the "built-in" apps... which include the Start Menu and Cortana) this involves running a command in PowerShell ... and lastly, 4) performing a System Reset saving personal files (which is basically a re-install of Windows 10 that saves your docs, pics, music, etc.... but doesn't save your programs (they have to be reinstalled).
The quickest try would be #3 ... it's a little messy looking (truthfully, the Windows built-in apps are my least favorite aspect of Windows 10 .. they need to improve) ... and it produces scary looking error messages while it's completing its job ... but it has worked (and worked quickly) for many users. If you'd like to try that method, the good part about it is that it should affect Steam or your current gameplay.
Here's how: Since your Start Menu isn't working, we'll navigate to PowerShell "the long way"
1)
Right-click your
Taskbar, and select
Task Manager.
2) From the
File drop-down menu, select
Run New Task.
3) In the
Create New Task window that opens, type
powershell and place a
checkmark in the box
Create this task with administrative privileges.
4) And select
OK.
5) At the prompt PS C:\Windows\System32> copy and paste in the following command
Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}
The apps will download and install within a few minutes ... you'll see the messy red errors (usually a non-issue) - you can ignore these .... once the process has completed, restart Windows ..
... and (hopefully) enjoy your working Start Menu and Cortana again.
.... Good luck!
[P.S. ... If this method doesn't work, you can try the more thorough SFC and DISM method next. I can give the step by step instructions for that, or you can follow the steps (with screenshots) from a handy online article
Has your Windows 10 Start menu stopped working? Here are four ways to fix it - B
By the way, screenshots of the PowerShell commands are also in that article.]