My main machine is a 24" iMac 7,1 and recently the fans have started up after boot up and within 30 minutes the screen goes out. At this point the computer is no operable, I've tried remote network connections and nothing. I ran the Apple Diagnostics on it and got the code: 4sns/40000000: TGOH. The last 4 letters there tell the story that its a temperature sensor on the GPU. Is it worth buying a new GPU and installing it? They run around $250 and I just don't know if I care. Probably time to get a 5k right? Riiight????