Strange Graphics Problem in Games

Odd graphics problem -- when playing virtually any FPS, my player perspective flips every 30 seconds or so. Rather than looking ahead, I'll suddenly be looking at the ground, or behind me, or up at the sky. This is true whether I'm using a keyboard and mouse (I've tried both wired and wireless) or a Steam controller, and it happens regardless of any input I"ve made. It's true whether the game is on Origin, or Uplay, on Steam or otherwise. These are not stolen or bootlegged games. I've ensured that I haven't screwed up the settings by accident; they're all at default. I've unplugged peripherals to eliminate potential conflicts and the problem persists.

I have an i5 2320 at 3GHz, 10 GB RAM, Win 10 64-bit, and a Nvidia 750ti GPU. The games I'm using are older ones, like SniperGhost Warrior 2, Rainbow 6 Vegas 2, Battlefield Bad Company 2, all of which are well within the limits of this system. Controls are fine in other games like Total War, etc.

Would sure appreciate some insight into this.

Thanks!