Originally Posted by ChrisSlicks

If the computer starts freezing up hard, i.e. no response, frozen screen, then typically in my experience this is a hardware problem. Check that the cooling fans for the CPU and graphics card are functioning correctly, I've seen the fans go out in as little as one year in a dusty furry environment. If the computer was recently moved around then consider re-seating the CPU with a clean and fresh layer of thermal paste and re-seat the add-in cards.