I use my Dell PC daily. It had a C: drive hard disk crash (and replacement) in July. This issue predates that crash, however.
My PC will (sometimes) lock up while I'm away from it overnight or for 20 or 30 minutes or several hours. At these times, it does not "wake up" when the mouse is moved or the keys are pressed. However, the lights are still on. And (lately at least), I hear the "going down" sound from Skype (or Windows?) when I press the power button to reboot it.
I hate doing these hard boots to it, but don't know how else to deal with nothing on the screen and no response. Not even Cntl-Alt-Delete brings up anything.
It's still running Windows 8.1, but I plan to upgrade to Windows 10 any time now. What could cause this?