|Is this systema desktop/tower or a laptop?|
If the latter then I'd be inclined to keep a close eye on it and if possible have the internal connections checked - especially with regard to the cd/dvd unit. Likewise the HD slot/position...
Equally if desktop etc... - if you comfortable going inside the case - should the problem re-occur - remove all mains power in (disconnect the mains cable/plug out from the back of the system entirely...) and carefully check "all" connectors. Not just teh ribbons and internal power connections to the drives, but any other plug/socket connectors too.
Then restore power and see what happens..
The experience you just had didn't happen without cause...; and it is useful (wise?) to have measures in mind should it re-occur. Also ensure you copy all data off the system (regularly) to external media - be it opticals or another HD. This if only to ensure that, should the worst happen..., your data at least is safeguarded - en-avance (ahead of time/event).