My Asus TimelineX running W7 sometimes does that, about once month. As you say the machine does not respond to any kind of input and I have to power it off by holding down the power button. All is then back to normal although it is very rare that it subsequently performs a diskcheck.
I have sometimes found that when it is unresponsive that if I wait 5/10 minutes it does come back to life.
Not very much to help you I'm afraid, but perhaps it is nice to know you are not alone.