My Dell Latitude 620 laptop lost all sound - all the devices for audio in device mgr had problems - I uninstalled and reinstalled all, also downloaded sigmatel and other drivers - still get "no audio device" if i click on sound, if i click on sigmatel get "device is inaccessible" - message for all sound components is code39 Windows can't load the device drivers - any ideas? Thanks!

Download the proper chipset driverto that laptop before installing sound drivers.

You might have to back up your data and reinstall windows.Based on what you've done it would seem that windows is corupted and preventing the driver software from loading.
good luck

Open the Device manager and click on the plus sign next to the "Sound, video and game controllers" to view all the installed audio devices. Right click on each audio device and click uninstall.

After uninstalling all the audio devices from the Device Manager, it's required to restart the Computer to complete uninstallation. If Windows Vista is running on the Computer then check the delete files checkbox on the confim uninstall window.

After restarting the Computer, reinstall all the latest audio driver along with any updates compatible to the installed Operating System.

It's required to restart the Computer after each installation of file to ensure successful installation.

You can download all the latest audio driver for the installed Operating System using the link given below:

http://supportapj.dell.com/support/downloads/driverslist.aspx?c=in&l=en&s=gen&ServiceTag=&SystemID=LATITUDE%20D620&os=WW1&osl=en&catid=&impid=