WSUS 3.0: Can’t view my network computers

When I click the computers section of my WSUS 3.0 administration console, my detail pane does not show any computers. I tried with “Any” in the “Status” drop down and clicked “refresh”. Nothing appears in the detail pane. On the top it shows “All Computers (0 computers of 0 shown, 0 total). Can some one help me troubleshoot this???

Further when we set GPO’s do we set them on the Domain Controller or the Server we installed WSUS on??