The Multimedia Audio Controller is part of your PC's sound system.  This is also usually associated with the Integrated (on the motherboard) sound and are installed when you install the sound drivers. 

If you do have the Integrated audio, HERE is the Dell drivers.  Depending on what has been done to the PC, e.g. if there was a complete install you may also need the Intel Chipset Drivers, HERE   The chipset drivers setup the Intel motherboard chipset and define what is on or attached to the motherboard. 

If you have a different, separate, sound card, you will have to find out what sound card you have in order to download the correct drivers, as Dell had two other sound card options, a SoundBlaster and a Turtle Beach (Voyetra).  Other drivers HERE

But, regardless of which sound you have, you MUST use Dell drivers because of their custom sound cards.

For future reference, with a complete reinstall the install sequence is (1) Install Windows (2) install chipset drivers (3) Install device drivers (e.g. sound, video, etc).

you need to check if you have the integrated sound card or a seprate sound card is installed in your system. As you explained that you get sound from the speakers but not while you play any video, so try updating the codec pack from this link http://www.free-codecs.com/K_lite_codec_pack_download.htm 

Download and install the one which says "Download [ K-Lite Codec Pack 4.2.5 Basic ]". Follow the prompts and restart the system. IT SHOULD FIX....

Not hardly :smileyvery-happy: .

Actually it leads to an interesting question - do Dell Diagnostics work with Dell-installed PCI sound cards?  I didn't think so, but I really don't know.  But I better not hijack any more of Suzy's thread :) .