|Assuming the audio is enabled and the speakers are good and properly connected then the lack of sound is probably due to drivers not being installed. You can check that in device manager. You should be able to download the drivers from the motherboard or system manufacturer's site or, if it's an add-on card, from the card or card controller chip manufacturer.|
If you think you deleted something that's affecting your ability to download it would be helpful to know what you were doing when you suspect it got deleted.
If it's possibly just a setting that got altered and you can't get it back to where it was you may be able to do a system restore from before it happened.