A couple of weeks ago my MacBookPro 8,1 early 2011 with a sandisk 256 SSD wouldn't boot. I have ran the Apple Hardware test many times and everything checks out fine, but even when I restore from the Time Machine or even Clone using CCC the MacBook won't boot from the SSD. I have now got an old fujitzu mechanical 120GB HD and the MacBook runs fine from this now.

The SSD can read and write as a normal external drive when connected via docking station so why can't I boot from it? I have tried formating using APFS as well as os x journaled (GUID)...but to no avail!