Why is my Xbox turning itself off?

About a month and a half ago my xbox would start shutting off randomly after playing on it for about 15-20 minutes. At first, I thought it was overheating but I don’t think that’s the issue (I never got any messages saying it was). I’ve moved it to a more open environment so it wouldn’t overheat, I cleared out all the dust in it, and I started using another outlet but it still shuts off. I’m not sure if it’s doing this because it’s old (I got it a year after xbox one released) or because of something else. Please help!!