Now I can't play mp3 files with Media Player, VLC Media Player or anything else
Can't play is a lot different then can't hear.... which is it?
If you can't hear, then right click the speaker ICON in he notification area and choose "PlaybackDevices" then in the resultant window with the playback tab selected make sure your "speakers" are selected as the "Default Device", (little green circle with a check in it), if not right click and choose it (set as default).
Then highlight speakers and click the properties button, select the advanced tab and start changing the sampling rates using the drop down arrow and then the test button until you don't get an error and you hear the test tone coming out of your speakers.
This is assuming you have everything connected properly and the correct driver for your sound card installed.