My computer

Hello,

I can start up my computer and it will take me to my background then i can do anything with it being slow for about 5 or so minutes then it just randomly restarts on it's own. i was originally thinking about just erasing everything and installing it again but should i do that? And if so how do i do this with so little time to do it in? What is wrong with it? And how do i fix it? and when and if it does get fixed how can i prevent this from happening again?

Thanks for all your help