Prohibitory sign 3 times at start, then it boot and works well
Few months back, (i think after El Capitán), when I power on my iMac, when the apple icon should appear, it shows a prohibitory sign and stays there a few seconds. Then the apple icon appears.
This occurs two more times, and when the apple icon appear the third time, it shows the normal loading bar and OS X boot as always. Then the computer works completely fine.
There is another problem, that I don't know if is related. Three months ago I checked the S.M.A.R.T. of my devices and I noticed that even with "PASSED" status, the HDD (secondary), fails in the Airflow Temperature Celsius field, showing around 60 degrees every time, even if I just turned on my computer. This HDD also have 37000 working hours, so I'm a bit scared.
Knowing this, yesterday I did an Apple Hardware Test. In the quick mode of this test it showed an error with the code "4MOT/4/4000003: HDD-1525". Looking in some forums I see references about HDD temperature (related to the 4MOT/4/4000003 part, HDD-1525 seems to be another thing I don't know).
So now, I don't know what I should do, cause I think the error on the airflow temperature field of the S.M.A.R.T. could be caused by a failing sensor, because it happens since a long time and even with the computer just turned on. I also don't know if the error showed on the Apple Hardware Test is related with the S.M.A.R.T. error (which is a thing a test could do).