Chosen Solution
My iMac shows black screen at startup and repeatedly chimes (normal chime - not the diagnostic beeps) until I press the power key again to switch it off. Have tried (with USB keyboard) resetting SMC, resetting PRAM/NVRAM, entering safe mode etc (as here https://www.howtogeek.com/189104/trouble...). No success. Still same problem. Any thoughts? Thank you David
@davidbaker, see Help with iMac reboot loop which goes over the same issue you’re experiencing. It’s most likely an issue with the GPU, as explained in the thread. Hope this helps! -Alex
