iMac will only boot through Target Boot Mode
Apple iMac 2011 EMC 2429
I have a 2011 27" iMac. It crashed an all I saw was the flashing folder with the ?. Put it in target disk mode and connected it to a brand new iMac. Opened using disk utility and saw that the drive was failing. Purchased and installed a new hard drive and got it running again by installing El Capitan via Target Disk mode(so I could use it as a 2nd monitor for my new Mac), but then the fan started to run all the time and I realized the new hard drive didn't have the thermo sensor, so ordered the cable adapter. While I waited for that to come, the computer ended up restarting itself, but then got stuck on the Apple logo with half the progress bar complete. It would go to a black screen then to a white/gray screen and then try to reboot itself over and over and over.
I put it in Target Disk Mode and was able to reboot it from my new iMac okay, but can't get it to boot on its own. Any ideas on what's going on and how to fix it?
I want to be able to use the old iMac as a 2nd monitor for me new iMac, so really I just need it to boot up. Please help!
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