Remove the battery and power lead then hold down the power button for more than five seconds. Then replace the battery and power lead and try starting. This will reset the power management settings back to default - they may have some how got corrupted.
If this does not work try switching on whilst holding down CMD, ALT, P and R. Do not release these keys until you have heard the chime noise a second time then allow it to restart normally. This will reset any corrupted display setting etc. that might be preventing a normal start up.
Hope one of these fixes your problem.
As stated by a previous poster switching on whilst holding the track pad button down should cause the DVD drive to eject after a few seconds - do not release the button until the drive actually ejects. This is probably not your problem though (unless the DVD in the drive is a recognised start up disk).