Mac does not show up in icloud devices - tried all troubleshooting steps

I've tried everything but my Mac OS 10.7.5 does not show up in "Find my iPhone" in icloud online. I erased this Mac once before a few months ago using icloud and want to do so again, but it won't show up. My iPad and other Mac show up when I turn "Find my mac" on, but this device does not show up. Location services on the device is turned on and the device is on a WiFi network (same as my other Mac and iPad). Help!

Thanks.