Diagnostic test won't work....

[Nothingfaced]

my imac is having an issue with the screen blacking out randomly, and I have tried to run the diagnostic test but it doesn't work.

I'll reboot, hold "D", and it simply takes a lot longer than normal to boot up to my regular login menu. No diagnostic test to be found.

What am I doing wrong?

 

[Weaselboy]

What year model is your iMac. How the test is run varies my age. Give this a look.