Why isnt my center speaker and surround sound working?

Because you don't understand the difference between stereo & surround sound.

For basic audio sources, most likely the Samsung does not have "Dolby Pro Logic" decode.

That's the system used with "stereo" media to support surround; unfortunately many cheaper surround units only decode digital surround like AC3 or DTS.

For movies that have surround audio, make sure the PC speaker settings (in control panel / sound) match what the home theatre system has.

You then need codecs that support bitstreaming to an external digital system..

See the article here for installing the LAV codecs & enable the appropriate bitstream formats in the audio decoder.

http://www.thehtpc.net/htpc-tips-and-tweaks/media-...

In the "filter tweaker", set every possible option in the first screen to LAV and disable all Microsoft options in the other two sections; that ensures all audio is passed to the bitstream system.

That should give proper audio from movies that have digital surround, when played via MS Media Player.

(Which should also now support all possible file formats, though you will have to confirm it's use with such as MVK).

You still may not get surround from youtube due to the way web browsers route audio; much of the system used by separate media players is bypassed. There again you may for some files depending on the audio type.