Tip for MacBook Not Sleeping
Eleanor Spenceley
I've been able to 'fix' two MacBooks (Pre Unibody) which failed to sleep after the lid is closed.Once you've exhausted all the typical diagnosis options like reseting of the PRAM/PMU, reinstall of the OS etc... and concluded the problem is a hardware issue.
Try this...
Open up your MacBook to get to the motherboard (here's a useful guide: http://www.ifixit.com/Guide/Installing-MacBook-Core-2-Duo-Upper-Case/515/2)
Now look at Step 15 (http://www.ifixit.com/Guide/MacBook-Core-Duo-Logic-Board-Replacement/296/5#s1136) Just to the _left_ of the red circle in the picture (and below the last port), gently press the small 'board' there. (Of course ensuring you are fully earthed before doing so).
Reassemble and with fingers crossed, try sleeping your MacBook.
Worked for me!!!!