software center - 'Some index files failed to download' while updating

When running sudo apt-get update I get these following errors:

Err archive.ubuntu.com quantal InRelease

Err archive.ubuntu.com quantal-updates InRelease
Err archive.ubuntu.com quantal-backports InRelease
Err archive.ubuntu.com quantal-security InRelease
Err archive.ubuntu.com quantal Release.gpg
  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]
Err archive.ubuntu.com quantal-updates Release.gpg
  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]
Err archive.ubuntu.com quantal-backports Release.gpg
  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]
Err archive.ubuntu.com quantal-security Release.gpg

  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]
Reading package lists... Done
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal/InRelease  
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal-updates/InRelease  
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal-backports/InRelease  
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal-security/InRelease  
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal/Release.gpg  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal-updates/Release.gpg  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal-backports/Release.gpg  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]
W: Failed to fetch archive.ubuntu.com/ubuntu/dists/quantal-security/Release.gpg  Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.177 80]

W: Some index files failed to download. They have been ignored, or old ones used instead.

I am using Ubuntu 12.04.
This is the command I used after installing Ubuntu from window installer.
I am sure my laptop is connected to internet. What can I do now?

Just open synaptic manager, install/reinstall ubuntu-extras-keyring and then (in terminal) type sudo apt-get update.

cheers u'd get out from this error.