try this don't know if it will help.
apply Win 7 default the first one in the list (Windows Aero) then run Ccleaner and any other cleaner and Spy ware you have. restart PC
then apply a WB Skin... if no go.
If you can try a system Restore a day or 2 before it happened.
did you install any programs that do anything to you taskbar.. if so uninstall them...
did you add any context menu to the registry or (as in did you edit in Regedit) if so undo them
Example: I used (Disable Full Row Select Windows 7) and some WB skins will not let me use the Explorer Backgrounds in WB's
undid it but still will not let me ...
hope something here will help good luck...