Hi there, I have a refurbished Dell optiplex 280. It was working fine until a few weeks ago I loaded Avast Anti Virus. Then the whole system went craxy. I managed to reload windows but then the sound wouldnt work. I downloaded the sound drivers from the Dell website but still it doesnt work!! Before the system crash the sound and video worked perfectly. I have now upgraded to Windows 7 to try and get the sound to work, same thing. I keep getting the error message "no sound devices installed" I have speakers that are working perfectly! Please help