Not sure if your Mac is using Intel or PowerPC processors?
1. In the Finder, choose About This Mac from the Apple menu.
2. Look at the Processor line to see which kind of processor is in your Mac.
|Press C during startup||Start up from a bootable CD, DVD, or USB thumb drive (such as OS X install media).|
|Press D during startup||Start up in Apple Hardware Test (AHT).|
|Press Option-Command-P-R until you hear startup sound a second time||Reset NVRAM|
|Press Option during startup||Start up in Startup Manager, where you can select an OS X volume or network volume to start from.|
|Press Eject, F12, or hold the mouse or trackpad button||Ejects any removable media, such as an optical disc.|
|Press N during startup||Attempt to start up from a compatible network server (NetBoot).|
|Press T during startup||Start up in Target Disk Mode.|
|Press Shift during startup||Start up in Safe Boot mode and temporarily disable login items.|
|Press Command-V during startup||Start up in Verbose mode.|
|Press Command-S during startup||Start up in Single-User mode.|
|Press Option-N during startup||Start from a NetBoot server using the default boot image.|
|Press Command-R during startup||Start from the OS X Recovery System1|