i was upgrading my mac mini to tiger(all my other macs are already upgraded, so i thought i'd do it with this one too)it was already loading then the electricity went out and back again...so the mac switched off..i tried opening it,it wont.. then after an hour or so, it did..but then i just get the logo and the loading circle...i tried the apllecommand+s.. it wont work..what do i have to do?