Before anyone responds with "Alienware is overpriced", save it. That's not the issue. I've had my X51 for a few months and all has been well up until last Monday. Since then the computer has started behaving strangely, displaying video errors when I'm (mainly) playing games.
This first happened whilst playing Civilization 5 whereby after [insert random period of time] the screen flashed with distorted pixels of black, white and hues of purple, then kick me out of the program displaying an error message.
This has now extended to League of Legends and almost any other program that uses Direct X (even the Windows Experience Index). However, instead of kicking me out of the program, Windows freezes and a forced reboot is needed.
Monitor and cables have been checked and changed. Diagnostic programs PASS everything, even CPU/GPU/memory stress testing. Up-to-date drivers installed. Most recent bios flashed. No new hardware added or removed recently.