not able to update ubuntu or install apps in ubuntu 12.04 LTS

Question

When I try to update using

sudo apt-get update  

I get error

W: Failed to fetch bzip2:/var/lib/apt/lists/partial/archive.canonical.com_ubuntu_dists_precise_partner_binary-i386_Packages  Hash Sum mismatch

And if I try to install any app the error I get is,

The following packages have unmet dependencies:
icedtea-7-jre-jamvm : Depends: openjdk-7-jre-headless (= 7u55-2.4.7-1ubuntu1~0.12.04.2) but 7u65-2.5.1-4ubuntu1~0.12.04.2 is to be installed
 openjdk-7-jre : Depends: openjdk-7-jre-headless (= 7u55-2.4.7-1ubuntu1~0.12.04.2) but 7u65-2.5.1-4ubuntu1~0.12.04.2 is to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).  

I already referred some solutions that were given for similar problems such as,

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

and

sudo rm /var/lib/apt/lists/* -vf
sudo apt-get clean  

Not able to proceed with some solutions since update or installing is not possible.
What may be the reason for this problem and how can a resolve this?

Answer 1

Backup your source.list:

cp /etc/apt/sources.list ~/sourcesBK.list

Download the "example repositories":

wget https://help.ubuntu.com/12.04/sample/sources.list

and reemplace yours:

sudo cp sources.list /etc/apt/sources.list

And try to make an update:

sudo apt-get update && sudo apt-get upgrade