I had the problem with Sketchup version8 on an I7 computer with windows 7 Ultimate "out of the box installation". New drawing, make rectangle and then try to push a cube did not work. Only the rectangle moved, no 3D expansion. After some experimenting on several computers I found that the mouse/keyboard driver is causing the problem I had. Deinstall  Microsoft's Intelli keybord and mouse driver. (Removing these programs from Configuration/software/remove, then reboot with standard HID drivers from w7. The problem with the push-pull tool is over. hope this helps you.