That is very strange. I cannot decide what advice to give you since there does not seem to be any common thread to the problems.
The next time each of these things happen, take a screenshot and post it.
If you had described the Start button problem without mentioning any other problems I would have advised you to go to the computer / display card maker's website and download then install the latest display driver. If you already have the latest one then reinstall it. On balance, I think it is worth doing that even though the other problems exist. You might have to use another computer to download the display driver to since your own is playing up then copy to your own computer with a USB stick.
The display driver fix
might help with the blank command window but I do not understand why its behaviour would be any different when you try to open it as Admin.
I would not expect the display driver fix to have any effect on the Task mgr or downloading problems. Get the display driver bit out of the way first and then, if you can get an Admin command prompt up and running, run
SFC.
- If SFC reports unrepairable errors then see my post
my consolidated ditty on SFC errors [WD update problem] - TenForums for the method of extracting detailed SFC results from the "CBS.log" file.
- Look further down
my consolidated ... post to see the picture of the unrepairable errors caused by a current WD update problem. If your SFC results match those then do not worry about them at the moment [if ever] because they are not related to the symptoms you have described.
- If SFC reports other unrepairable errors then check you are connected to the internet and use the command
Dism /Online /Cleanup-Image /RestoreHealth in an Admin command window [this is noted in both the tutorial & my consolidated ... post]. Afterwards, run SFC again.
- If SFC eventually reports no further errors then try your problem issues again - Task mgr, downloads, ...
- I am not certain that this will help fix the faults you report but given that they are purely Windows 10 problems [rather than being associated only with applications] it might do so.
Post back with details of what happened, what has been fixed, what faults still occur.
Best of luck,
Denis