I have a mid2012 13" MacBook Pro when I start it it has a circle with a slash through it. I have tested the the hard drive and its ok. I installed two different brand new solid state hard drives into it. After installing the OS on them I get the same circle with the slash through it. I took a hard drive cable from another mid-2012 MacBook Pro and I get the same results. I swapped the hard drive cable on the non-working MacBook Pro to another laptop and it worked great. Since I know the hard drives and hard drive cables are good what do you think is causing my problem? Thank you for looking.