Windows 7: NO audio output device

anyone help me.. i changed my os from xp to windows 7... but now same as the problems of the others, no audio output device with a red mark on the icon.. i just installed the cd windows 7. i cant install my graphics card because it says it's not supported with windows 7.. so i can open windows media center and i cant play music too.. pls help me.. i lost my cd for the motherboard also... can anybody help me? pls..

After looking at you specs I really need to know what CPU you are running, whether you are using an internal sound card (on mother board), or PCI card, and if so the manufacture, and the age of the card. The sound card may not be supported either. Also even if you are running a 32 bit version of Win 7 512 of ram is just a might to low. You system would run a lot smoother with 2 gigs.