Macbook wakes from sleep with lid closed/ wont stay shut down

I have a late 2008 Aluminum body macbook that they discontinued because it was basically the same as the pro only 200 dollars cheaper .

The problem I'm having is that the computer won't stay asleep. I can shut the lid and it will sleep for a few seconds and then the apple lights up and the hard drive makes noises. it will then go back to sleep, and then fire back up and repeat. I also tried using the sleep feature in the apple menu and left the lid open. This also fires the computer back up. Also, when I shut the computer down- lid closed or open, It turns itself on after a few seconds. I tried resetting the SMC using this guide that the Apple care # automated system gave me: http://support.apple.com/kb/HT3964
(of course this WOULD be the only apple product i dont have apple care on)

This is not a HUGE deal, but it is nonetheless annoying, and I've only had this for two years, so I'm not ready to replace. The waking is understandably obliterating my battery life.

I did notice one way to get the computer to STAY shut down. If i shut down the computer and then hurry and take the battery out and put the battery back in, it will stay shut down. BUT i shouldnt have to do this every time just in order to save battery.

HELP!

 

i tried that. going to the apple menu in the top left corner and selecting sleep. It still wakes up

 

Sorry, i overlooked the article at first. I went through the article and paid special attention to look over the main causes of sleep problems at the bottom. Still, my computer is an insomniac. Thanks for the reference though. Other ideas?

 

could it be a software problem? If so, How could i diagnose which programs keep it from sleeping?