Check the SD card slot for damage to the plastic, and that the connections are all slightly raised.
Try holding the card in place while booting. A few people have said their cards don't seem to fit very well.
Does the green ACT LED do anything when you power it up? (Glow very faintly, flicker briefly, not light up at all).
Can you see the boot files on the card when you put it into another computer? There should be a smallish (about 56MB) partition that Windows and OSX can access.
Actually, scratch all that. I've just noticed that you said:
bskill wrote:Have tried 2012-12-16-wheezy-raspbian
That image
won't work on any new Pi that has a Hynix chip on it. Look at the top of the main chip and you should see "Hynix" in small letters. (If you see "Samsung" ignore this bit and go back to my original points). For the Hynix chip you need to use the 2013-02-09-wheezy-raspbian, otherwise you will get exactly the symptoms you described.