have you set it to shut down after being inactive for so long, for instance if you are going out to make a cup of coffee or answering the door, is it in sleep/hibernate mode, just check your settings,then what are you using like windows 10 or whatever if you give this kind of information it would help, the make of the computer isn't necessarily the problem, it's the software - so if you could give that information you get a better answer to help troubloeshoot