Ok.... I believe my Stuffit Expander app has been corrupted. I think my son was messing at one point and it started not opening files. I updated it at Alladin but this did not work. (version 8) So, I completly ditched the app and installed an older version from a friends mac.(version 7) .Sit files open sometimes while .dmg files do nothing at all. Stuffit launches and does nada. I've dragged files into the window, double clicked, everything. Now software updates like ichat av in .dmg cannot open. I just tried Garageband too, and nothing! Help anyone? I.