thais1979 wrote:
After choosing an account through the login screen, my iMac desktop produces a flashing bright screen intermittent with a black screen, never turning on. I have shut it down several times, completely unplugging it and waiting several minutes, to no avail. Any ideas?
To trouble shoot further you can:
—SafeBoot How to use safe mode on your Mac - Apple Support
Takes a bit longer to get to the login screen, does a quick disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc.
Login and test. Reboot as normal and test. Caches get rebuilt automatically.
In Safe mode third party system modifications and system accelerations are disabled, it removes malware, etc hampering smooth operation, however a reboot will put it back to normal mode.
This test will tell you if third party interference; extensions etc are not loaded in safe boot mode.
If your Mac starts up to a blank screen (white, black, gray, or blue)
If your Mac starts up to a blank screen - Apple Support
if no insight or resolve—
Call Customer Support (800) MY–APPLE (800–692–7753)
or on line Apple Support