Hi,
Check to see if there are any red crosses or yellow exclamation marks against your audio device in Device Manager.
To check go to
'''Start''' > '''Control Panel '''> '''Device Manager''' > '''Sound, Video and Game Controllers'''. click on '''+''' to expand.
or
'''Start''' > '''Control Panel '''> '''Hardware and Sound''' > '''Device Manager''' > '''Sound, Video and Game Controllers ''', click on '''+''' to expand.
Your audio device should be listed here. It should say ''Sound Max Integrated Digital HD Audio''
If it has a red cross next to it, right click on it and the click ''enable''. Then see if your audio works.
If it has a yellow exclamation mark next to it, right click on it, click on ''properties'' In the ''General'' tab there is a status box which probably says that the device is not working properly. Click on the ''Driver'' tab, click on ''Update Driver'', click on ''Browse my computer for driver software''.
Before you proceed you need to download the Win7 audio drivers from this link. Make sure you select the correct OS http://www.driverscape.com/manufacturers/dell/laptops-desktops/optiplex-755/119
Once you have downloaded the drivers (only the '''Audio '''drivers and remember where you have downloaded them to) go back to Device Manager and proceed with the driver update by browsing to where you you have saved them and then following the prompts.
After the driver has been installed there should be no crosses or marks in Device manager and hopefully your sound will work.
If there is no listing under Sound, Video and Game Controllers check under '''Other Devices''' if it is there apply the driver updates the same way and it will be put in the correct place.