If you have mp3 player or something similar, even tv should be fine, you can test your speakers plugging them to some of thoseand test if there is sound, if there is problem is in computer and if there is not speakers are faulty, also it is good to check what Einnol stated.
Also if speakers are ok, try to remember when you last time heard sound, then try to remember when you noticed sound was gone, after that make note everything you did with computer, I have managed to do some things that I had no recall at all, but going back this way I have been able to isolate problem to enough narrow area to be found.
I did work bit over four years in customer support and computer repairing and it was quite uncommon to have fault in audio hardware, however not impossible, anyway best thing to do is to start from most simple thing and then eliminate possibilities one by one until you have found problem, worst thing to do is try this and that and maybe even that one there