Samsung Galaxy Grand Prime (2015) Frequent Shutdowns & Restart Loop with Colored Dots Screen

I have had a Samsung Galaxy Grand Prime for some time since the summer of 2015. The phone has no scratches on the outside, it is not dirty at all. I always wear covers for the front and back, as well as the foil. But the problem is one! for 4 days I have been struggling with the fact that the phone often turns off several times in two minutes, as if it turned on again. Then there is the Samsung inscription, colors are flying around it, the black background turns on and the Samsung inscription and the dots that are flying again towards this inscription on a black background and on this Phone stops, I do not want to turn on or off I need to remove the entire cover from the phone and again Samsung with dots I do not know what it may depend on ... the phone has never flooded or was not damaged did not fall. Please help

Is it not overheating in these housings?
I have LG X Power and it heats up, and Xperia also restarted once. Reset your phone settings and we'll see.

I would diagnose it as follows:
1. Factory default reset - test if something has helped, if not:
2. Downloading the whole ROM again - also test or help.
If these 2 methods above do nothing, then the fault is on the hardware side.
It can also be a symptom of a damaged battery. Take a look or have it bulged. You write that you have it for 2 years and from experience I know that batteries very rarely last for such a long period.

And when you put the batteries in, it starts itself or do you need to press the switch?

It is possible that you have a short circuit on the power button.