My answer applied to 'Snow Leopard' OS X 10.6 only.
Since you're using the newer 'Lion' OS X 10.7, the procedure I detailed does not apply to Lion.
Here is a link to the current Lion OS X 10.7.4 Combo update. It's huge, 1.4GB, so downloading will take a while.
http://support.apple.com/kb/DL1524
If that doesn't work, perhaps this Lion Recovery page would help:
http://support.apple.com/kb/HT4718
I'm not on Lion, so I can't offer much assistance.
Most threads I found about reinstalling Lion depend upon the App Store working in order to re-download and reinstall, and obviously that won't help when the App Store is not working.
Message was edited by: kostby