Last week, I was gone for almost an hour, and my computer tower shut off. I turned it on, the boot screen showed, and my tabs were still up. It did it again this week. Then, the other day, when I was helping my mom get furniture, it fell asleep. When I moved the mouse to wake it up, it made the noise it makes when I shut it off by pressing the power button on the tower and shut off. It turned on again after I pressed the button, and went to the boot screen, and my tabs were saved. Should I be worried?