Now I can't start the Ubuntu Software app.

For diagnostic purposes please provide the output of the following commands (to be executed in a terminal window):

uname -a
lsb_release -crid
sudo apt-get update
sudo apt-get dist-upgrade
ubuntu-software

ramsing@ramsing-Latitude-E5510:~$ uname -a
Linux ramsing-Latitude-E5510 4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:01:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
ramsing@ramsing-Latitude-E5510:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 16.04.1 LTS
Release: 16.04
Codename: xenial
ramsing@ramsing-Latitude-E5510:~$ sudo apt-get update
[sudo] adgangskode for ramsing:
Havde:1 http://dk.archive.ubuntu.com/ubuntu xenial InRelease
Havde:2 http://dk.archive.ubuntu.com/ubuntu xenial-updates InRelease
Havde:3 http://dk.archive.ubuntu.com/ubuntu xenial-backports InRelease
Havde:4 http://security.ubuntu.com/ubuntu xenial-security InRelease
Indlæser pakkelisterne... Færdig
ramsing@ramsing-Latitude-E5510:~$ sudo apt-get dist-upgrade ubuntu-software
Indlæser pakkelisterne... Færdig
Opbygger afhængighedstræ
Læser tilstandsoplysninger... Færdig
ubuntu-software is already the newest version (3.20.1+git20160617.1.0440874.ubuntu-xenial-0ubuntu1~16.04.1).
ubuntu-software sat til manuelt installeret.
Beregner opgraderingen... Færdig
Følgende pakker blev installeret automatisk, og behøves ikke længere:
  linux-headers-4.4.0-31 linux-headers-4.4.0-31-generic
  linux-image-4.4.0-31-generic linux-image-extra-4.4.0-31-generic
Brug »sudo apt autoremove« til at fjerne dem.
0 opgraderes, 0 nyinstalleres, 0 afinstalleres og 0 opgraderes ikke.
ramsing@ramsing-Latitude-E5510:~$ ^C
ramsing@ramsing-Latitude-E5510:~$

That should have been two separate commands

sudo apt-get dist-upgrade

ubuntu-software

Please try again.

ramsing@ramsing-Latitude-E5510:~$ uname -a
Linux ramsing-Latitude-E5510 4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:01:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
ramsing@ramsing-Latitude-E5510:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 16.04.1 LTS
Release: 16.04
Codename: xenial
ramsing@ramsing-Latitude-E5510:~$ sudo apt-get update
[sudo] adgangskode for ramsing:
Havde:1 http://dk.archive.ubuntu.com/ubuntu xenial InRelease
Havde:2 http://dk.archive.ubuntu.com/ubuntu xenial-updates InRelease
Havde:3 http://dk.archive.ubuntu.com/ubuntu xenial-backports InRelease
Havde:4 http://security.ubuntu.com/ubuntu xenial-security InRelease
Indlæser pakkelisterne... Færdig
ramsing@ramsing-Latitude-E5510:~$ sudo apt-get dist-upgrade
Indlæser pakkelisterne... Færdig
Opbygger afhængighedstræ
Læser tilstandsoplysninger... Færdig
Beregner opgraderingen... Færdig
Følgende pakker blev installeret automatisk, og behøves ikke længere:
  linux-headers-4.4.0-31 linux-headers-4.4.0-31-generic
  linux-image-4.4.0-31-generic linux-image-extra-4.4.0-31-generic
Brug »sudo apt autoremove« til at fjerne dem.
0 opgraderes, 0 nyinstalleres, 0 afinstalleres og 0 opgraderes ikke.
ramsing@ramsing-Latitude-E5510:~$ ubuntu-software

When you started ubuntu-software from the command window, did you see some new window on screen?

No. It only shows the rotating ("hour-glass") thing for about 6 seconds. Then it turns off and nothing happens.

Is there any output in the command terminal window?

No.
(I had a similar problem 2 years ago. An installation (mscorefonts) failed, and it caused constant problems afterwards. The only solution was to reinstall Ubuntu. No command in the terminal could fix the problem.)
When I switch to guest account, everything is fine. But downloads from that account can't be used in my masteraccount.
I appreciate your efforts and hope for a solution, but it seems that the access to Ubuntu Software is blogged - the system continuously tries to finish the installation without success. Could you uninstall the app Ubuntu Software? And then reinstall.
As I said earlier, I managed to install Gimp in the terminal afterwards, so access by terminal works.

I just tried installing GIMP on another ubuntu machine. No wifi problems this time, but installation failed again. Tried to do it from Ubuntu Software app. Also failed from command terminal window.
Could there be a problem with GIMP?

Your output does not show any problem with package management. The problem seems to be just with ubuntu-software and/or its related packages.

There is Bug #1606238 where several other people report a similar problem.
You might try the workaround given there:
rm -rf ~/.local/share/gnome-software/

Remark: The command to uninstall and reinstall the Ubuntu Software package and its key dependencies would be:
sudo apt-get install --reinstall ubuntu-software gnome-software gnome-software-common

Sorry. I tried all your suggestions, but nothing solved the problem. I ended up reinstalling the whole thing. At least with Ubuntu - that's not a big deal.

Hi Mark

Thank you very much. I'll try that next time
Thanks for all your efforts at this forum

Christian Ramsing Lund

> Den 7. sep. 2016 kl. 13.48 skrev Mark Rijckenberg <email address hidden>:
>
> Your question #381192 on Ubuntu changed:
> https://answers.launchpad.net/ubuntu/+question/381192
>
> Mark Rijckenberg proposed the following answer:
> Next time, try executing step 10 in the following procedure instead of
> reinstalling Ubuntu:
>
> https://help.ubuntu.com/community/PackageManagerTroubleshootingProcedure
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/ubuntu/+question/381192/+confirm?answer_id=11
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/ubuntu/+question/381192
>
> You received this question notification because you asked the question.

Thanks Mark Rijckenberg, that solved my question.

I have the same same issue and it still fails even after doing a complete NEW compete re-instal of the entire OS. I am so frustrated that nothing can keep this app working that I will now have to decide what other OS to install/ You and the rest of the Ubuntu people ignore this problem and I an giving up on Ubuntu. It should not happen and is not fixed and may never be.