Cannot Access Start Menu On Win 10

I have a problem on a PC I updated from Win 7 to Win 10 last week. I cannot access the Start Menu. I think I have used the correct term. On the bottom left hand corner, at the far left edge of the Task Bar is the Windows symbol. I cannot attach an image*. If you left click it a menu should appear. When I do nothing happens.

I have had no other problems with this PC since installing Win 10, but I am tempted to roll it back to Win 7. I updated another PC to Win 10 and that had Win 8.1 and that is fine. But, this one seems very sluggish. I don’t know if not being able to click on the Windows button and have nothing happen is going to be the start of a raft of problems or a one off.

*I cannot attach an image because I wanted to access Paint but in doing so have also discovered that the search button to the right on the Windows symbol on the Task Bar is not working. Everything else on the Task Bar, being links to software programmes, are working.

 

I suggest you do a sfc /scannow on that system but you must do it via a command prompt (admin) and the best way to do that is right click the bottom far left windows tile and choose 'command prompt (admin)' then type in:
sfc /scannow (make sure you leave the one space after sfc)

It may take some time to complete, so make sure no programs are open at all on the system when you do it, then leave it to complete.
See here for how to get a text document report of the scan - don't even bother with a cbs.log

"To view the details that included in the CBS.Log file, you can copy the information to the Sfcdetails.txt file by using the Findstr command, and then view the details in the Sfcdetails.txt. To do this, follow these steps:

1. Open an elevated command prompt as described in the previous step 1.
2. At the command prompt, type the following command, and then press ENTER:
   findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log >"%userprofile%\Desktop\sfcdetails.txt"
   
   NB: I posted this at same time as DavidGp.

 

Thank you both for your advice. The problem is fixed. I'm not sure how. I ran the troubleshooter to which David linked as it seemed the easiest option to try first. The Troubleshooter told me that there were missing applications but not what they were and that it couldn't help any more. Afterwards I decided to ignore the stupid thing and turn it off and try again tomorrow. Instead for some reason I restarted and after the restart the start menu is back.

As you can see from the attached immage to the right of the Windows button it is a grey area with "Search Windows" there. Prior to this issue I had a maginfying glass symbol. Is there anyway I can change back to that?

 

Here's the image that should have been attached to Post #5.

 

I've downloaded the book. Whether I'll understand it is another question. Thanks anyway.