Computer did something strange

My desktop computer did something strange yesterday. It was on, not being used, and I was on the floor nearby plugging a cable from the TV into the wall when I heard the computer just shut off. The power to the surge protector didn't turn off or anything and none of the plugs to the computer came loose, the computer just turned off on its own. Then, I noticed that the "on" light on the front of the computer, which is green when the computer is on, was flashing orange. I got out my laptop to try to look up information on what might be happening, but couldn't find much. One site suggested the motherboard might be fried. I did the only reasonable advice I could find, which was to take out the RAM and put it back in. There was also a lot of dust on the heat sink for the processor and on the power supply, so I cleaned that off, too. Then I turned the computer on and it booted up in safe mode. I had unplugged the mouse and keyboard previously and they weren't recognized when I plugged them back in, so I just had to shut down the computer. Today the computer seems to be working fine, but I wonder if it's going to do this again. I wish I had some idea of what might have caused this.