Over the past week my computer has been freezing and restarting without warning. This does not seem to be a BSOD, as I've had trouble with one before and that used to stay on the screen until I restarted: this automatically restarts. First I thought it was random, but all of 4 times have been whilst playing various games on Steam. Each time also seemed to be in response to an action within the game: I click on something in the menu - freeze and restart; I get killed in-game - freeze and restart. My computer is powerful enough to run all the games I have on full graphics setting and I have never had any trouble like this before; it is recent and has only started within the last week or so. What on earth is going on?