Chosen Solution
When i turn my computer on it makes initial start up sound then turns off after about 3 seconds.
Try booting from your system install disk. Plug the computer in so it’s got plenty of power. Insert the disk part way then hit the start button then push the disk all the way in. Hold down The “C” key. Let me know what happens.
Does this turn off about at the apple screen with the rotating gear? If so you may be looking at a corrupted system file. To test this you should boot to the OS install disk and run disk utility to try and repair the volume.
Try turning it on with the charger connected, you may have a bad battery.
