I don't know, it can be due to things breaking, but it could also be a memory dump error or even a virus. My old 4.2GB HD acting as the C: drive and as the windows OS started bluescreening frequently a month or so back - it could have been dying a death (after all I did use that HD for 3 or so years before it was temporarily taken out and then put back in for extra space) but it could also been caused by over tweaking the settings or even a virus, as when I got a new hard drive this december my 24GB D: drive (my 2nd oldest in my computer) was infected by blaster and nachi and another worm (very unpleasant).
The steps I would take depends on what is happening, as suggested by other people above as well.
1. If this error has happened just the once, then I wouldn't worry about it (OSes do crash, even XP although its rare) but I would keep your eye open for further bluescreens.
2. If the same error bugs you frequently, run an anti-virus check to detect any virii that might have invaded Gengis Kahn like your PC - a virus attack although not as brutal and fatally sudden as marauding barbarian hordes can still feel very sharp and very pointed
3. If it still crashes, it could be the hardware, and you will need to look at the things Zedric suggests, like the memory, drivers etc.
Hopefully this should bring up what the problem is, but if you still need help post it here and I and I am sure others will try and help