Uses of the phrasal-verb "settle down"

One could let what one had learn "settle" but that would not mean more studying but giving yourself a break to let you absorb what you had already studied. To settle down to studying means to stop whatever was preventing you and get to work.

to become quiet and begin giving one's attention to something

Emphasis mine.

You might use it for the computer in the sense

to become quiet, calm, or orderly

but only if the computer had been acting in a bizarre and random manner.

As for the symptoms, that would be unusual. One would refer to the body or organ as settling down if it could be described as acting up before. One would not say that one's headache or head had settled down, but if you suffer from an upset stomach, a treatment might make the stomach settle down.