Black screen at startup, chimes repeat every two seconds, nothing more
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.