Q: Problem re-installing OS on my Mid 2009 Macbook Pro

So.. I have a mid 2009 MBP, It originally shipped with Snow Leopard and I have upgraded OS every time a new one came out. No sooner had I installed El Capitan then I started having problems. The unit wouldn't wake after being shut for 30 mins, I would have to hard reset (hold power button down for 10 seconds) then I started getting random messages about apple involked agent something or another... and needless to say it wouldn't boot.

So I decided to re-install Snow Leopard as that is the only disc I have. So I first of all removed the SSD that was in there (yes I had uprgraded it last year) I put it in a portable hard drive enclosure and plugged it into my imac and transferred all my needed files, then I re-formatted (I did this because none of the recovery options on the mac book pro worked, so I figured a fresh install would be best. I formatted with default settings, 1 partition GUID named OSX I then took the drive and put it back in my MBP and turned it on, the snow leopard install pages started to show up but when it got to the select hard drive section, at first no drive showed up? I removed the SSD again and re-formatted the same way just in case I had done it wrong and then put it back and tried again, this time it showed the hard drive but it was greyed out so I could not select it, then all of a sudden it disappeared and wouldn't shoe up again. I tried yet again and this time it showed up, but the installation froze up about 5 mins into the installation.

I'm trying to figure out what the issue could be, at first I suspected a dodgy hard drive connector, but that doesn't seem to be it.

I welcome any suggestions, i'm getting ready to chuck this thing out a window!... seriously!