What causes a computer to reboot on its own?

Mary’s computer keeps rebooting by itself
My computer has been acting up recently. I have reinstalled the operating system many times due to it rebooting when turned on. When I did get it to work, it stopped and I got a message that it couldn’t find the hard drive. I have given up on it and don’t know what to do to get it to work properly. I have Avast antivirus installed on it and have for a long time. Could you please help me? My hard drive has been somewhat sounding different, but I am not sure if this is the problem. Any help would be appreciated. Thanks

Our answer
We’re just guessing here, but normally when a computer reboots itself for no apparent reason it’s because the processor is overheating. This could indicate your cooling fans are not working, the air vents are clogged, or you have a problem with your motherboard. Thankfully, the first two reasons are the most common.

Make sure your vents are not blocked by dust. Dust can accumulate over time no matter how clean your home is. If they’re partially blocked by dust your processor will overheat and shut your computer down or reboot it. It’s a safety feature to keep your processor from being damaged by excessive heat. If the air vents in your computer’s case are clear, then your cooling fan or fan(s) are probably not working – or not working correctly. In that case you’ll have to install a new fan (not expensive) or have someone else do it for you (not too expensive).

It might be your hard drive too, but we doubt it. It’s much more likely to be the processor becoming overheated. However, if your hard drive is making strange noises that is a symptom that usually indicates it’s going bad. We are well aware of this because we’ve had it happen several times. This first indication something was amiss for us was when the hard drives started making strange noises – not loud – but very noticeable. Since you seem to be comfortable installing Windows, you might want to install a new hard drive, especially if your computer is four or more years old. Installing a hard drive isn’t difficult to do – but if you don’t feel comfortable doing it, it is not too expensive to have one installed. Most hard drives come with simple installation instructions, and in most newer computers the hard drives just slide right in. If you don’t feel comfortable installing a new hard drive, it should not be very expensive to have one installed.

We hope this helps you.