A few days ago I started to have an unusual pattern on my PC. It turned off it's screen but I could still hear the processor and fans
points to graphics problem - driver - screen cable - or screen - or graphics chip.
(going out from my pc for a couple of minutes), closing my notebook (when I reopened it, the notebook wasn't sleep or hibernating, it was in this weird bugged state)
check power options in widows and BIOS make sure it is set not to turn off the screen