Had the same problem .... fans running, dvd spinning, sleep light glowing, no chime/no start. tried all the fixes here and whadayaknow Tomas Jones, Feb 16 2012 fix made it boot! That was holding down the cd eject key while (trying) to start up. The DVD ejected and it started on the HD. Then I turned up the muted volume and restarted and it chimes!
when you try to power on does the sleep light come on? If so you might remove the memory and try to start up. I am no expert but I have read that bad memory will do this (power connector lit and sleep light on but no boot) If the memory is at fault (I read) it will beep beep. If it does the same thing the logic board is suspect. (I'm just parroting what I read today) :O)