First of all, make sure that the sound is not accidentally muted.
If the sounds seem to play, it means that your speaker cables are faulty or have some kind of break in them. Or, your speakers or the electronics inside them developed some kind of fault.
Unplug the speakers and the speaker cables and test them on another computer. If they work fine on another computer, the problem could be your sound drivers. You could also test the sounds, using a headphone in place of the speakers. If you can hear the sounds fine with the headphones, the problem is with the speakers or the cables.
This may be less likely since the sounds seem to play, but it's still possible that your sound driver is incorrect or not the one meant for your sound card.
Start the Device Manager (Right-click My Computer -> Properties -> Hardware -> Device Manager) and under the "Sound, video and game controllers", see that the sound driver is listed.
Double click the item in that list that contains the word "audio device" in its name. Does Device Manager say that the device is working properly? If Device Manager says that the audio device is not working properly, or if there is a yellow exclamation mark next to the device, or if it says that the drivers are not installed for this device, install the drivers from the CDs or from the laptop manufacturer's website. However, there's an easier way to do this, as given below.
Here's the easy way to get or update your sound drivers:
You could try to use this driver scanning tool, which scans the computer for needed drivers and has an option to automatically retrieve them for you.
You can download this free tool from here
or directly from this link
After you have downloaded the above file, double-click on it and follow the simple steps to install it. Then, when it asks if you want to run it, just answer yes. This is easier than manually searching, downloading and installing the drivers.
If, after trying with the above method, sound still can't be heard, you can try with the System Restore. To know more about System Restore, go to this link
If none of the above methods worked, pull out your sound card and test it in another computer. You can also try re-installing Windows and lastly try another sound card, if it still fails to work.
Hope that helps,