I have re installed OS many times(XP PRO) sound was working.

Last time I have Windows 7 Ultimate ,Sound was working.
I have formatted Windows7 (C drive only) and installed windows XP again,installed SP2 then SP3. Installed drivers.this time I don't have sound in my system.
Control Panel> Sounds and Audio Devices> shows No Audio Device .
Device Manager shows Yellow Mark on Sound driver "Realtek High Definition Audio".

Please help me to get sound back on my system.

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Regards
Narasimha