so I RARELY shut my computer off (doesnt remember last time I shut it off)

ive changed the date and time twice now

last week i was convinced was a day it wasn't for such a long time

when i woke up today the clock was off by 3 hours and 6 minutes but when i went to bed both my clocks was same time it didnt reboot it self because everything i left open was still open

how do i make my computer Clock STAY to what ever its set with out auto changing itself ?