BSODs are unbelievably difficult to diagnose.
As DU said - if it doesn't happen again, don't worry about it - probably just a stray cosmic ray.
If it does happen again, then firstly you need to try to see if there's any pattern in the occurrences - that may give a clue is to what is causing it.
Now, if it seems totally random, then it's most likely a hardware issue.
BUT, a software issue is easier to diagnose and fix - if there's a pattern to when it BSOD - say it's a case of it only ever does it when you open application X, then reinstall application X.
If it appears to be a part of windows, or there either seems to be a pattern, but you can't discern what software is causing it, or it's random, then do a complete reinstall of windows, make sure all your drivers are up-to-date, and then install any additional apps/games/etc.
If after all that, you still get the same BSOD, then it's hardware.
And this is where it gets tricky - cos it could be any single component causing the problem - the only way to work out which it is is to swap each one out, and then back in, one at a time until the BSOD goes away.
Finally if the BSODs are random and different each time, and you get other weird random behaviour, suspect your PSU.