I have installed new Ubuntu 11.04 from .iso file but when I try to run
sudo apt-get update
It gives me following error.
Failed to fetch http://us.archive.ubuntu.com/ubuntu/...source/Sources 404 not found [IP: 81.189.88.40 80]
Failed to fetch http://us.archive.ubuntu.com/ubuntu/...-i386/Packages 404 not found [IP: 81.189.88.40 80]
Failed to fetch http://us.archive.ubuntu.com/ubuntu/...-i386/Packages 404 not found [IP: 81.189.88.40 80]
Failed to fetch http://us.archive.ubuntu.com/ubuntu/...-i386/Packages 404 not found [IP: 81.189.88.40 80]
Failed to fetch http://us.archive.ubuntu.com/ubuntu/...-i386/Packages 404 not found [IP: 81.189.88.40 80]


I have tried all these but it does not solve my problem.I am still facing errors.
sudo rm /var/lib/apt/lists/* -vf
sudo apt-get update
sudo dpkg --clear-avail
sudo dpkg --configure -a
sudo apt-get clean
sudo apt-get update

My internet connection is perfect. I am able to open all sites.

I am not able to download any software from Ubuntu-software center.
It shows error - "Failed to download repository information"
I am not able to install software using terminal by install command.
It shows error - "Unable to locate Package"
Synaptic package manager is not able to fix broken packages because the "apply" button is disabled and mark for installation or re-installation is also disabled.It is not able to download new package information neither repository.
It shows "Could not download all repository indexes"

Please solve my problem.

Post you sources list:

I got the solution of this problem.

I have changed the mirror.
1. Go to software sources.
2. select First tab : ubuntu software
3. change the mirror : Download from & select another server like main server or another country's.

Another temporary solution is
change the /etc/apt directory. change this with another same version of ubuntu.
But this is not that much easy if you are doing installation at home instead of LAN.