Imac Keeps Rebooting Over Over Won T Fully Boot Has Lines On Lcd Imac Intel 24 Emc 2134 And 2211

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iMac keeps rebooting over and over. It won’t fully boot and has vertical lines on LCD screen Sound chirps… Apple logo comes up with loading bar… gets about 1/2 way then reboots. Does this over and over again. 24" iMac 3.06 GHz, 2x2GB (4GB) & NVIDIA GPU (Model A1225)

Check the diagnostic LEDs to the left of the RAM slots. Sounds like a failing GPU, which can be replaced or reflowed. This guide, though slightly different will instruct you on how to replace it: iMac Intel 24" EMC 2267 Graphics Card Replacement