Q: Aborted startup

While downloading to the current version 10.11.4 my old Powerbook (6 y.o.) it suddenly shut itself off.  I then tried to restart it.  I managed to type in my password and got it started up to halfway in the upstart process, seen in the horizontal bar, then the Powerbook just turns itself off again!

Half a year ago I changed out my old 500 GB HD with a new hybrid drive comprising of a 8 GB SDD and a 1 TB HD.  To accommodate this I purchased a Sandberg USB 3.0 Multi Hard Disk Link with Crucial Easy Laptop Install Kit where the software was the issue. 

I eventually managed to mirror the old disk onto the new one and it has been working fine with the new SDHD since until I tried to update the operating system, yesterday.

So today I connected the old HD from the Powerbook via the Sandberg Link.  Starting the Powerbook again holding down the option key (alt) gave me the options of starting it from both of the HD now connected, the internal one as well as the external one.  But even if I chose to start the Powerbook from the old HD it failed to start up properly!  It followed the same startup path and shut down at about half way in the upstart procedure!  Has anyone any idea what can cause this and what remedy there is to cure it? 

Regards

William