Would appreciate any guidance on the following:

-I am running Ubuntu 12.04 LTS
-An icon consisting of a red exclamation point has appeared on the horizonal desktop bar, and tells me update information is outdated
-When running update manager, updates are downloaded. But appear to fail to install. I do not always get an error message, but
Update manager tells me last update was some time in the past, even though I have just run an update.

The original cause of my troubles began when I rashly deleted some files to fix a perceived earlier problem:

sudo rm /var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_precise-updates_restricted_i18n_Translation-en
sudo rm /var/lib/apt/lists/extras.ubuntu.com_ubuntu_dists_precise_main_binary-i386_Packages

Any guidance on how to get my updates working again would be greatly appreciated. Thank you.