No sound from my speaker.?

Hi I am a 27 years old girl I need your help. My PC was having some problem in booting, so I fix it by pressing F8 at start up & using last known good configuration. My PC is now booting normally but now I am having sound card problem. WMP is showing error message that my sound device is not installed or it is being used by another programme. I dont know how to fix the problem. Add or Remove Programs is showing my sound drivers installed. Please help me.