When you ran MVT it gave you a report number. Can you post it here please?
When you open Security Center does the page display Am I Protected or does it display Your Computer Is Secure? This info will help us to identify which version you have.
Moved to SecurityCenter 9 as he speaks of left hand menu and that was only in the old application.
As Peter says you have the 2009 version. AT&T have not upgraded yet. To confim bottom right corner is there an About or Details link that shows you the versions?
I would suggest an uninstall reinstall as we all have the 2010 version and it is hard to remember the 2009 1. Your other PCs are fine so a uninstall reinstall would be the first thing I would try.