You need to post a lot more than that in order to troubleshoot. Error messages, other symptoms, what you were doing at the time, what kind of computer you have, etc.
It could be anything. I dare not even hazard a guess. Although, faulty power would certainly cause that problem. I won't even diagnose a client's machine with something happening that infrequently. It's near impossible to track it down on the bench, because it is near impossible to make the problem repeat itself at will.