(See summary above) ... The computer went dead (black screen) and I had to do a hard boot to get the computer back up and running. When I went back into my game, my area has created a approx. 40 x 40 hole in my area that could not be accessed. The game crashed again. Now the game continues to crash when I go back in, whether it is a private or external server game.

Update (30/11/2012 ... 1150hrs): I haven't done anything but it appears that I can create a new game and play in it without the game crashing. Unlike before, I can now also access the server game as well without the game crashing. As for my other 2 private games (one is a hardcore and the other is the one that I had the crash on), accessing those games causes the game to crash to the Minecraft Crash Report Page. I have not included another crash report for now as the new ones appears to be like the others attached below.

What I expected to happen was...:
Not crash.

Have included the 3 crash reports from my system for you attention