Current status

I've started to suspect this is not an Ubuntu issue, but related to the internet connection here at my work. Until I'm sure, Im leaving my question below:

Original question

I'm stuck, can't upgrade my system. Running sudo apt-get upgrade gives me the following:

mmm@alalunga:~$ sudo apt-get upgrade 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages have been kept back:
  ginn libgrip0 linux-generic-pae linux-headers-generic-pae linux-image-generic-pae
The following packages will be upgraded:
  apport apport-gtk bind9-host build-essential dhcp3-client dhcp3-common dnsutils eog evince evince-common firefox firefox-branding firefox-dbg firefox-globalmenu
  firefox-gnome-support firefox-locale-en gimp gimp-data gir1.2-totem-1.0 glib-networking glib-networking-common glib-networking-services gnupg gpgv
  icedtea-6-jre-cacao icedtea-6-jre-jamvm icedtea-6-plugin icedtea-netx icedtea-netx-common icedtea-plugin isc-dhcp-client isc-dhcp-common libapache2-mod-php5
  libart-2.0-2 libbind9-80 libdns81 libevince3-3 libgimp2.0 libisc83 libisccc80 libisccfg82 liblwres80 libssl-dev libssl-doc libssl1.0.0 libtotem0 linux-firmware
  linux-libc-dev openjdk-6-jre openjdk-6-jre-headless openjdk-6-jre-lib openssl php-pear php5-cli php5-common php5-curl php5-dev php5-gd php5-mysql php5-xsl
  policykit-1-gnome python-apport python-django python-gst0.10 python-problem-report resolvconf thunderbird thunderbird-globalmenu thunderbird-gnome-support totem
  totem-common totem-mozilla totem-plugins xserver-xorg-input-synaptics
74 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
Need to get 317 MB/327 MB of archives.
After this operation, 1.481 kB of additional disk space will be used.
Do you want to continue [Y/n]? 
Get:1 http://archive.ubuntu.com/ubuntu/ precise-updates/main openjdk-6-jre-headless i386 6b24-1.11.4-1ubuntu0.12.04.1 [27,3 MB]
Get:2 http://archive.ubuntu.com/ubuntu/ precise-updates/main openjdk-6-jre-headless i386 6b24-1.11.4-1ubuntu0.12.04.1 [27,3 MB]                                       
Get:3 http://archive.ubuntu.com/ubuntu/ precise-updates/main openjdk-6-jre-headless i386 6b24-1.11.4-1ubuntu0.12.04.1 [27,3 MB]                                       
Get:4 http://archive.ubuntu.com/ubuntu/ precise-updates/main openjdk-6-jre-headless i386 6b24-1.11.4-1ubuntu0.12.04.1 [27,3 MB]                                       
Get:5 http://archive.ubuntu.com/ubuntu/ precise-updates/main openjdk-6-jre-headless i386 6b24-1.11.4-1ubuntu0.12.04.1 [27,3 MB]                                       
Get:6 http://archive.ubuntu.com/ubuntu/ precise-updates/main openjdk-6-jre-headless i386 6b24-1.11.4-1ubuntu0.12.04.1 [27,3 MB]                                       
Get:7 http://archive.ubuntu.com/ubuntu/ precise-updates/main openjdk-6-jre-headless i386 6b24-1.11.4-1ubuntu0.12.04.1 [27,3 MB]                                       
9% [7 openjdk-6-jre-headless 27,3 MB/27,3 MB 100%]

It keeps downloading the package openjdk-6-jre-headless, then does nothing for a while (hanging on what's the last line above), then download the package again. It's at its 13th download attempt at the moment of writing. The actual downloads seem to be done just fine, but whatever it does after downloading seems to be failing.

I tried removing openjdk-6, but then it wanted to install openjdk-7 instead, with the same result, hanging at openjdk-7-jre-headless instead.

I also tried changing servers from my local (Danish) to the main server. No luck.

It's also keeping me from upgrading alle the other packages.

What to do?

Update

After following instructions in the answer by @lpanebr, it is now stuck at the linux-firmware package. So, maybe it's a more general problem than being related to specific package(s)? Although it did download some packages without problems before getting stuck at linux-firmware.