There can be a few factors that cause your laptop sound to function erratically. It is often a software issue but sometimes even hardware problems can cause this malfunction.
If it is a software problem, it is almost always due to driver problems. In such a case, it is better to get the latest soundcard drivers from the laptop or soundcard manufacturer. The drivers on the laptop manufacturer’s website may not be the latest and so a better idea is to get your driver downloads from the soundcard manufacturer’s website.
If it is a hardware issue, then it may be that you need to take your laptop apart to fix the hardware related sound problem.
In laptops, soundcards are located on motherboards and so it is not possible to replace them. You might find a genius who can replace the soundcard chip on a laptop but that doesn’t often happen and even if it does, such geniuses wouldn’t want to spend their time on something so inconsequential (for them) as a soundcard chip replacement.
If you can still hear the sound through one speaker, then the problem can be fixed easily. You will have to take your laptop apart, but maybe it will be enough to just remove its plastic cover near the keyboard. All this depends on the model of the laptop. A better idea would be to search for instructions specific to your laptop model (you could find these on the Internet) and then follow them to the letter.
So, where do you get the speakers to replace them? EBay is certainly the best place. You can actually get any laptop related part on eBay.
Another problem could be that your operating system is not compatible with your laptop hardware. This often happens right after an operating system upgrade. In such a case, there is an additional soundcard that you may connect to the laptop, which is known as the PCMCIA card which has audio inputs. You can get these on eBay as well. These cards are often better than the card you get on the laptop’s motherboard when you purchase it. They are often available with 5.1 channels.