Currently Being ModeratedFeb 2, 2013 4:51 AM (in response to MomoMac)
The question mark shows that your Mac couldn't find any bootable volumes, and in most of the cases, it's a sign of a hard drive problem.
First, press the Option key while your Mac is starting and choose Macintosh HD. Maybe your Mac forgot the startup disk.
If it doesn't show up, insert the Mac OS X DVD, press C key while your Mac is starting and try reinstalling OS X. If you can't, the hard drive is damaged, so take the Mac to an Apple Store
Currently Being ModeratedFeb 2, 2013 5:33 AM (in response to MomoMac)
What version of OS X are you running?
If it is Lion or later you do not have a OS X DVD in that case you will need to boot from the recovery partition.
Hold the command and R keys down while starting your machine. See OS X: About OS X Recovery
Post back if you have more questions.