IPhone 4S keeps turning off and on?

I've fixed another problem on the phone where it would just loop the white apple logo turning off and on.

Now it just randomly turns off and on, even after trying a system reset.

Any suggestions to fix it?

Try a DFU, search it on Google. It involves holding down the home and power button for a certain amount of time, cannot recall the exact steps, but just do a quick Google search!

Just check your phone hold ( lock ) button.

Hold the Off key button on top… Until it completely shuts-down. Wait a few minuntes & turn on, see if that helps.
Good luck