(adsbygoogle = window.adsbygoogle || []).push({}); Here are some combinations of keys that you can use will booting your mac, if you are having troubles:

[command + v] - Verbose boot, shows what files are loading, useful if all you see is the "pinwheel" forever.
[t] - Target disk mode, turns Mac into an external hard drive, firewire only, useful for retrieving files.

     - Boot from CD or DVD

[d] - (While Install DVD 1 is in drive) Starts Apple Hardware Test

[mouse button held down] or [eject] or [f12]- Ejects all removable media

[command + s] - Single user mode

[command + option + p + r] - Resets parameter RAM. Mostly voodoo, but never hurts.

[command + o + f] - (PowerPC Macs only) boots into Open Firmware

[option] - Display boot menu

Shift (On boot) - Safe boot, loads no kernel extensions

Shift (On login) - Safe login, doesn't launch startup apps

[Command + r] - Boots to Recovery Partition in Lion ONLY



Hope these Help!