Try the following:


With the computer OFF:

Reset the PRAM by pressing the power button then IMMEDIATELY hold down the Option-Command-"P" and "R" keys until the computer reboots (and the screen goes black) THEN let go of the keys. Do not let go of the four buttons until the computer reboots. (If you do this correctly (with the four buttons being held down almost immediately after turning the computer on) your computer will reboot.)

If you don't have the timing correct, it will boot up as before with the flashing folder and question mark. Turn the computer back off and retry the procedure.

If after successfully holding down the buttons, and your computer restarts, your computer MAY reboot again. Let it continue to boot until the apple icon appears on the center of the screen. If the Apple logo doesn't come up on the screen, try the next step.


With the computer OFF:

Press the power button then IMMEDIATELY hold down the option key. 

After a few moments, can you see your internal drive as an option? (It should show you an icon with the "Macintosh HD" below it.)  If you don't see any icons after booting with the option key being held dow, then it's safe to assume the hard drive has died. 


If the steps above do not solve your problem, you MAY be able to get the computer to work but the data you stored on that computer will be lost. To do this, reboot the computer and hold down the "N" key until a picture of a globe appears on the screen. Once you see the globe, let go of the "N" key and let the computer boot. If booting this way STILL doesn't work, then your computer has reached the end of its life. 
RIP Apple Computer. You have fought the good fight, You have finished the race, You have kept the faith.