I may not have good news for you, but this problem happens in different machines under different circumstances. The fix here may not solve your problem, but it’s totally harmless, so it deserves a try.
Hit WINDOWS+R key to fire up the “Run” dialog. Type “msconfig” and hit Enter.
Switch to “Boot” and select “Safe Boot”, followed by “Network”. You can do “Minimal if you want, but I like to authenticate my session using my live account. Both will work. Click okay and Restart your computer.
Your computer will restart and you will enter automatically on Windows in Safe Mode. Meaning that many drivers and programs will not run. Your screen resolution will get funky. Don’t worry, just keep going and log in (if you have a login).
Click in your Start Menu. At this point, it should be fixed. You will be able to see your menu and your tiles again.
Repeat Step 1 to get back to the “msconfig”. Select “Boot” and uncheck “Safe Mode”, this way you will go back to your normal settings.
At this point, after you login back to Windows, you should be able to use your Start Menu and Cortana again. If not, I’m sorry that this workaround wasn’t for you, it’s very frustrating, but keep trying different tutorials, one might be for you.