How can I diagnose my MacBook Pro Start-up problem? I have a MacBook Pro 8,1 (Early 2011) / 8GB (2x4GB RAM) /256 SSD  and was running El Captain. One morning I couldn't boot it up. 

After doing the Apple Hardware Test which showed faulty RAM I put back my old 4GB (2x2GB) RAM sticks, retested and had no errors. I had all my data on an external drive so I did a complete restore back to Lion 10.7.5. After installing the system, the Spinning wheel of death appears very frequently, but I put that down the indexing which had a remaining time of 5 days. After rebooting the system once, I couldn't boot it again. 

I have done the hardware test multiple times since then and everything checks out fine. I have installed Lion twice since then also, but if I do a restart it never boots further than the grey Apple logo and spinning wheel  like the very first time. I have tried all start-up options. Safe-mode never boots. At the moment I am trying the "Choose Startup Disk" option and choose the partition but I only see the wheel of death. 

After doing a verbose boot, the system did infact reboot after approximately 3 hours. However, even just entering my login password brings back the spinning wheel of death which runs for a couple of minutes so that the mac is effectively useless and then "kernel panic".

How can I diagnose what is going on here? Processor, Permissions? Other problems?
Solution to my problem was to buy a new internal Sata 
cable. I could have spared myself a whole lot of trouble if I had done that at the start.