No sound

I recently had to reboot and reinstall everything on my computer Gateway 300X (0030074257) with windows xp home edition SP3, the sound was working before but now i have nothing.
sound device it says is Unimodem Half Duplex Audio Device
i also get the message Modem #0 line playback (emulated)
I have gone onto Gateway and tried to download the sound driver from there but don't get anywhere with it,
I have a big yellow question mark over Multi media audio controller,
under device manager, Sound, video and game controllers I have
Audio codecs
legacy audio drivers
legacy video capture devices
media control devices
uni modem half-duplex audio device
video codecs
and they are all working properly it says

Motherboard name Intel Brownsville D845GBV/BROWNSVILLE 2 D845GEBV2/REXBURG D845GRG/REXBURG 2 D845GERG2
MOTHERBOARD CHIPSET - INTEL BROOKDALE - G i845G

MULTI MEDIA
Audio Adapter - Intel 82801DB ICH4 - AC/97 Audio controller [B-0]

if you can help in anyway please let me know thank you

 

check out my post ,i had a similar problem . it might help
http://forums.majorgeeks.com/showthread.php?t=211327