I have dell Optiplex GX620, I have installed windows 7 but it shows that no audio output device is installed. I even changed my sound card, but no use. I have visited many hardware shops as well to repair it but no one could find any problem.
the tower should have a dell service tag # on it put it in the box in link and download drivers for the motherboard like chipset and video and sound .
if hands on computer repair people cound not fix it then there either don't know what they are doing or the computer broke beyond repair .adding another sound card should have fixed it as long as you installed drive fro the new card http://www.dell.com/support/troubleshooting/us/en/04/TroubleShooting/ProductSelector
the gx620 normally comes with a PCi card.was the old card ever working. one poster said to check the bios. you want to make sure the onboard is disabled.and enable the pci. if you still cannot get sound use another PCI slot (if you have one)alo make sure you are plugging into the speak/head phone slot on the PCI card. if the PCI card has a audio cable to connect to the moboo make that's connected too.
new window on gx620 and started using it but no sound now.
the new windows install likely didn't install drivers for the sound devive ,so unless you install the correct driver for the sound its no going to work,and like i said in my other post ,Dell computers have a service tag on them go to the link in my other post and put in theservice # and it will take you to the correct driver for the computer