I have a white Intel macbook with 4GB ram. Every time I try and shut down or restart the computer drops everything. The screen goes to the wallpaper, the mouse, the menu bar, and the dock disappear and the computer freezes. I don't have a pin wheel. So far I've tried to fix the disk permissions. And delete the Extensions.mkext file. The only thing that turns the computer off is by holding the power button down until the computer turns off. Where do I go next?