I have a 1.5 GHz PowerPC G4 running OS X v. 10.4.11. A few times recently I have been using it normally and a pop up box will appear. It will be totally blank except for the ok button. Not sure what to do, I hit the ok button and it went away. I ran disk utility and verify permissions (the only thing I really know how to do--not a mac expert) but it didn't seem to find anything. Any ideas.