I have a Powerbook G4 and tried to download a software update on Friday for Mac OS 10.4.11. The software did not download properly so I tried again. The same thing happened and my computer froze up. I restarted my computer and now OS X won't start. I can't do anything on that computer. What is going on? The window with the status bar for OS X is the only screen that will come up. Nothing happens.