Issue with MacBook on Boot I have a 2012 MacBook Pro 13" with a 500 gb SSD 

the SSD is about 1 year old and it was performing excellent, but now i dont know

Sometimes when i turn off the Mac and turn it on again im experiencing the Prohibitory sign on boot, i usually wait and sometimes the apple logo reappears or flashes a few times and then prohibitory sign appears again, sometimes i wait a few seconds and then it boots as normal

I have performed a Hardware test and it doesnt show any problem. I have reinstalled the OS a few times, SMART status is OK and i checked the disk with First aid on Disk Utility

Altough it always boots up, the prohibitory sign is making me nervous because im about to sell the MacBook and i dont want anything  to spoil my selling, i want to sell an excellent product.

The RAM is also in good shape so it is not that.

I checked SATA cable to see if something was loose, but nothing.

Any other suggestion?

EDIT 1

Also, sometimes it stays black after a wake up and i have to power it off and on to be able to use it
You might be experiencing an HDD cable failure.  I've had to replace a few of them from 2009-2012 laptops.  They run about $40CAD on Amazon; you'll need your exact model number to find a compatible one.  To find that, hold option, and go to Apple > System Information.  Look for the Model ID, it'll be something like


  MacBookPro11,2


Good luck!