Nightly Computer Crash

So, the past three mornings I've awakened to find that my computer "did not shut down correctly." That is, the computer is off, and when I hit the power button, I get the Safe Mode option screen. I have no idea where to even begin looking for this culprit. Could it be my power settings (I have a W-7 Pro 64 bit system, and it's set to "Balanced" ... the preconfig'd powers setting)? I've had this computer over a year and it's never done this, so I'm not sure if it's a new install (although I've not added any programs, but have updated a few) or what.

Any ideas where you'd start to look for this villain? This is a new one for me. Everything seems to be running fine once I'm back up, but it's happened every night after I've gone to bed, which is why I suspected power settings, but ...

Thanks for any suggestions you can offer!

Richard,

Thanks for your prompt reply. I do weekly complete virus scans, but will do a manual one today, as well as with my Malwarebytes. When you say "clean boot" do you mean just do a reboot before bed and then let it sit?

Ah, never mind on the "clean boot," I see the link. It didn't show up on my email notification, so was asking prematurely. Will try this out ...

BTW, I came home today after being gone for a few hours, and I had the same problem, so I'm really suspecting my power settings ...