My computer turns off by itself when it's been on for hours especially when I'm playing and watching videos. When I'm playing or watching videos, it will turn off by itself after maybe 10 or 15 minutes. Please help, this has been going on for 3 months now. THANK YOU!!!

You need to make sure it is clean of heat trapping dust and dirt. Also ensure it is free of malware. Note this could also be due to a failing PSU, failing RAM or failing motherboard. Start with cleaning and while in there make sure, all connections are tight and secure.