Currently Being ModeratedFeb 12, 2013 10:10 PM (in response to DisasterDr)
First, try checking that everything is connected and resetting the SMC > http://support.apple.com/kb/HT3964
If it doesn't work, I'm sorry but your computer is dead. You have to take the Mac to an Apple Store or reseller to get it repaired
Currently Being ModeratedFeb 17, 2013 8:55 AM (in response to DisasterDr)
A 2008 computer is likely to have an older PRAM battery that may need replacing. Those aren't that expensive to replace. http://www.ifixit.com/ has directions you can do so yourself.
Currently Being ModeratedFeb 17, 2013 8:56 AM (in response to a brody)
I might add, after 4 years most PRAM batteries start going bad, and they can prevent a machine from booting properly if they aren't relatively newer. Leaving it not plugged in for a period of time will prevent the computer from being able to reboot itself with the battery closed to death.