Windows Unexpected Shutdown

Siddhi_ thumbnail
Posted: 13 years ago
Yesterday when I was watching a show on YouTube, my screen suddenly went black, then the screen said Power Save Mode. After that the computer shutdown and restarted by itself. When I logged back on, a message came up (See Image). That was the first time something like that ever happened.
 
Today when I was watching shows the same thing happened again. I would keep logging on to continue watching the show and it would happen again after 10 minutes or so. It happened 4 times today.
 
I'm confused as to why this is happening. I run a full computer scan everyday and there are no viruses or anything.
 
This is the ONLY message I get when I log back on after the unexpected shutdown.
 
 
Any help / advice would be much appreciated. Thanks.