More and more this is sounding like a hardware problem.
What were the results of the diagnostics that I asked you to run?
If you haven't finished them, here's the link again: Hardware Diagnostics

You can boot to a USB drive that contains another (bootable) OS.
This may allow access to your files, so you may be able to back things up.
I'd ask about this in the General forums as I'm not real familiar with the options available.