Windows 7 Opening multdiple Windows Explorers

[tvzzz]

I need to have two copies of Windows Explorer open, so I can move stuff around efficiently. This has always worked for me. Today, I can't open a second copy. When I right-click the start button and select "Open Windows Explorer" (after opening one copy of Explorer), it just changes the shading on the copy I already have open. Any ideas? I'm running Windows 7 Home Premium. Thanks.