What do you have running in the background that shows up in the Task Manager when that happens?

Check the 'Applications' tab to see if anything else is running or showing up as 'not responding', if there is nothing else besides the game, then check the 'Processes' tab and look for the processes running under the current user's profile.

One other good place to check is the Event Viewer > Application logs:
Start > Run > eventvwr.msc > OK