My laptop has this problem where after a couple of hours it starts lagging to the point that its unusable. When I try to restart it, it just hangs on the "Restarting" screen. I always end up hard resetting it.
It's an Asus N53SN running Windows 8 at the moment. The problem started a couple months ago, when I was still running Windows 7.
Things I've done:
Format and re-install Windows 7
Sent it in to Asus, they reformatted it, re-installed Windows 7 and new drivers (That was useless, and I'm out of warranty now)
Format and install Windows 8