I've got a 2009 Core 2 Duo iMac that's refusing to boot. It just keeps displaying a white screen forever. Holding down the Alt key does not display boot options and holding down the PRAM-reset keys elicits no response. I've tried installing a different hard drive (I figured maybe it was short circuiting or something) and pulling one bar of ram and then the other. None of that makes any difference. I'm getting desperate and would appreciate any suggestions. Even just some way to confirm a dead logic board would be helpful, as I could then go ahead and order a replacement.