Sound card

when i first got the computer, i guess it had onboard sound, it is an emachines pc.the sound was working fine, until i deleted some stuff off the computer, and then i had some problems with my internet. so i had to go into safe mode, that's when the problems started with, the sound.every time i would go into the media player it would say, no audio device installed? is there something simple that i could do to get my sound back.