MacBook Pro will not start

Late 2011 MacBook Pro

16GB RAM

500GB HDD

My MacBook pro was acting normally until the shutdown options showed up for no reason and then without any user input it just shut down.

The battery was well above 75% at this point but I just left it to charge fully just in case.

It will not start without at SMC reset and then it will start up with the gray screen, not show anything and once it has checke3d the cd drive for a disk it will just click and shutdown again and then not respond to the power button without another SMC reset.

I removed the HDD and tried again...

This time the computer started up but the gray screen stayed on just blank with no logo or loading bar for a while so I held the power button down to shut it down.

I then got a new HDD and copied the old one onto the new one using Carbon Copy Clone and installed that.

The system is now behaving like it originally did where it will need an SMC reset and then will just shutdown after a few seconds of the startup. still not showing any logo, just making the chime sound.