Hope this helps.
For a user using multiple operating systems, holding down Apple Key + X during start up will force OS X to start.
- To use a startup disk other than the main one (i.e. on an external drive) hold down Apple Key + Option + Shift + Delete during start up.
To boot from a CD, hold down C during start up.
To start in Firewire Target Disk mode hold down T during start up. This turns your Macintosh into an external drive for another Macintosh, useful for data transfer.
To start in Safemode, hold down S during start up.
To start in Single-User mode hold down Apple Key + S during start up.
To reset PRAM, hold down Apple Key + Option + P + R (until you hear the chime sound for a second time). Use this in such scenarios when settings (like the time, etc) are not being remembered after a reboot.
Holding down Apple Key + S and then typing /sbin/fsck -fy at the prompt will force your Macintosh to run basic file system checks.
- Apple Key + Option + O + F and then typing eject cdat at the prompt will force your Macintosh to eject the CD.