How can I ride a bike having severe spinal disease and pain?
I would think some sort of a tricycle would be the best choice for you, probably a recumbent.

Something like this is the first thing that comes to mind:



You lay in a reclined position and pedal with your feet in front of you.  These come in several variants, from fully reclined (such as the above) to more upright.

There are also numerous variations of the hand-powered cycle, and some that are operated with both hands and feet such as this one:



Some of these are "stock", while others are fairly highly customized "one-off" bikes.  (But several versions of the basic tricycle recumbent are available "off the shelf" at relatively reasonable prices.)

I never seen any of these bike styles with an auxiliary motor, but I'm sure there are some.  Several battery-assist systems are available for standard bikes and could be easily adapted to a recumbent.  A full-power gasoline engine would be a bit more complicated.