So I have had this problem before but this is for my friend's mac that I am trying to fix...his mac 2012 13" is not detecting his hard drive... 1. his hdd works fine outside his mac, I attached it to an enclosure I can see it no issues. 2. I put in a new hdd to his mac it will not erase it properly, it will be stuck at 1/2 way point and will not progress and fail eventually. 3. I give up using his mac..i take out the new drive put it in the enclosure and I figure I format it with my mac, name it put it back into his mac and it should see it and it would be an easy install, no such luck, the installer will not see the HDD, disk utility will see it but with disk0s1, which is very weird because I partitioned it and named it etc on my mac and it was showing nicely and it is not showing on his mac... I checked the cables nothing that I can discern is wrong.. what else can I try?