crwdns2934241:0crwdne2934241:0 mayer

crwdns2934249:0crwdne2934249:0:

Here's Apples Service Source manual on your machine.  Page 204 shows the location of the diagnostic LEDs:  http://www.scribd.com/doc/47791656/59/iMac-20-inch-Mid-2007-—Lower-Exploded-View

crwdns2915684:0crwdne2915684:0:

open