Apple Mac mini (Intel-based; Mid 2007) - Manual (Page 31)

Chapter 3 Problem, Meet Solution 31
If your Mac mini freezes during startup or you see a flashing question mark
 Wait a few seconds. If your Mac mini doesn’t start up after a delay, shut down your
Mac mini by pressing and holding the power (®) button for about 5 seconds, until it
shuts down. Then hold down the Option key and press the power (®) button again
to start up your computer. Keep holding down the Option key until your Mac mini
starts up, then click the arrow under the icon of the hard disk you want to use as your
startup disk.
 After your Mac mini starts up, open System Preferences and click Startup Disk.
Select a local Mac OS X System folder.
 If the problem occurs frequently, you may need to reinstall your system software
(see “Reinstalling the Software That Came with Your Computer” on page 32).
If your Mac mini won’t turn on or start up
 Make sure the power cord is plugged into your Mac mini and into a functioning
power outlet.
 Press the power (®) button and immediately hold down the Command (x), Option,
P, and R keys on an Apple keyboard until you hear the startup sound a second time.
On other keyboards, press the power (®) button and immediately hold down the
Windows, Alt, P, and R keys.
 Unplug the power cord and wait at least 30 seconds. Plug the power cord back in
and press the power (®) button again to start up your Mac mini.
 See “Learning More, Service, and Support” on page 41 for information about
contacting Apple for service.