reinstall the audio drivers in device manager (search for how to get there on the googlinator)
Please be a little more specific?
PC sound, HD sound, all sound?
What OS, CPU, on board sound or sound card.
Why not try to fix what you have what is already on your computer before downloading anything else.
Its almost impossible to trouble shoot anything being such a vague description.
Run task manager to see if there are any drivers, what sound card/on board and codecs that are installed.