I have built my own PC,the motherboard being a Asus P5N-D and I have no sound at all,hope you can help

Did you install the audio drivers for that motherboard's audio chipset?

Yes

Check in Device manager if you see any ding on the sound card like yello ! Mark or red X...
Also please tell me if its an intigrated sound card or you have installed an external sound card...

Thanks for your reply but its working now,I must have touched something, thanks again.