[lubuntu] My installation is not updating

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http://ubuntuforums.org – So I haven't had internet at home for a few weeks now and when I try to update wherever I take my laptop where ever there's internet it does not let me. I tried to do it manually and this is the message that it is giving me. Code: W: GPG error: http://pr.archive.ubuntu.com raring Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <[email protected]> W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/raring/Release¬† W: Some index files failed to download. They have been ignored, or old ones used instead. E: (Hardware)