I am an 8th grader working as tech at my middle school, and one of the computers that I'm working with seems impossible to use. I needed to add an admin account to the computer, but the system preferences on the computer had the prohibitory sign on it and would not start. (I found the system preferences app in the trash, so I can guarantee that a student had something to do with this.) After one day of trying to find a way to get this to work, I turned on the computer the next day, and it would not boot. After a few moments of the Apple sign appearing on the screen, it would show the prohibitory sign again, and would not load anything. I got a 10.6.7 Snow Leopard install disc and put it in the computer, but it when I got to the install page, it would say that the computer can not finish the installation (this is on the main page of the installer). So I got a 10.6.3 Snow Leopard disk and it started the install process. I had started this during 4th period, but when I checked on it during 6th period (after classes), it said that the installation had failed. I used the Disk Utility from the Mac OS X Installer disk, but it said that the Macintosh HD had no problems. I went into Restore System From Backup but it did not have any Time Machine backups. When I have tried to boot into Safe Mode, nothing happens and it goes to the prohibitory sign again. When I try to boot into command prompt, I get a mach_kernel error and nothing happens. *** Command prompt just loaded regularly, but I am unable to use the classic hacks to get in (removing applesetupdone, changing password through Localhost%, or accessing com.apple.DirectoryServices.plist). To add to these problems, the bottom two rows do not work, so I am using a USB keyboard. If a iBook G4 keyboard would work, that might be a start to being able to use this computer. ANY help is appreciated with this. Thanks.