16.04 software download stuck pending

Try the following methods

From the command line

Try to install with the following command

sudo apt-get install the-program-package  # general
sudo apt-get install htop                 # example (small package)
sudo apt-get install libreoffice          # example (big package)

Text after the # character are comments (not used).

If there are problems, run the following commands.

Oldfred's command list for cleaning and repairing

#houseclean
sudo apt-get autoclean # only removes files that cannot be downloaded anymore (obsolete)
sudo apt-get clean

#refresh
sudo apt-get update #resync package index
sudo apt-get upgrade #newest versions of all packages, update must be run first

#would upgrade you to the latest kernel in the repositories
#dist-upgrade is also able to remove existing packages if required
sudo apt-get dist-upgrade

# fix Broken packages -f 
sudo apt-get -f install
sudo dpkg --configure -a

# Remove lock
# If you are absolutely sure you do not have another upgrade process running.
# Locked dpkg - only if sure you are not running another update.

sudo rm /var/lib/dpkg/lock
sudo dpkg --configure -a 

added zika's tip for problems with hash sum mismatch

sudo rm /var/lib/apt/lists/*
sudo apt-get update

added 2F4U's tips for Package Manager & Update Manager problems

Does executing these commands help?

cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get update

This will rebuild the cache.

If it doesn't help, this forum thread has additional suggestions:

http://ubuntuforums.org/showthread.php?t=1869890

Synaptic Package Manager

Try to install Synaptic with the following command lines

sudo add-apt-repository universe
sudo apt-get install synaptic

and start it

• from dash in standard Ubuntu or
• from menu - system tools in the other Ubuntu flavours (Kubuntu, Lubuntu, ... Xubuntu).

Synaptic is a little more difficult to use compared to Ubuntu Software, but Synaptic is a very powerful and reliable tool. If you manage to install it, I think that you will be able to use it to install the program packages, that you want to install.

Other repositories

It is also possible that you need some other repository to download the program packages that you want. Please edit your question to tell us which program packages, that you are trying to install.