No audio output devices are installed...:-(

Hello i have very very big problem with my sound i don't speak very good english so i just hope somebody will understand me and help me solve my problem...i don't have any audio output devices installed,everybody find solution in BIOS or in Device manager but i can't..even i don't have any questionmark anywhere.....when i check my computer everything is ok,everything is working properly and no problems are found...i don't have any sound,game or audio devices in device manager and i am getting crazy about it...i can't solve it.i tried everything..i had vista but my friend reinstall it to windows 7..after a while i started have problems with sound...please help,better