No sound even though it was working just yesterday. Help!

Hello everyone!
I'm having a big trouble with my windows 8. Yesterday I was watching a clip on YT and suddenly the sound stopped. I tried to restart the computer. I didn't work. The sound on YT is on full voulume as well as on my computer. Then I went to sound configurations. I clikc 'configure my speakers' and 'configure' then 'test' and I get a message that 'the sound can't be played'. I tried playing some music which is on my computer instead of playing music online and windows player says 'windows media player had found a trouble wile trying to play music'. I downloaded winamp but it didn't work as well. What is more I was sometimes using Ubuntu via Virtual Machine and the sound had been playing ok but when I tried to play sth today it was silent... Of course I googled the problem up and read what Microsoft says I should do in this situation (check the sound card, ect. I did it, downloaded the program attached to the tutorial and the program found no errors). The issue can't be due to reinstalling my system - my computer is one week old, it was bought brand new it has never fallen down or anything. One more thing. Yesterday out of blue moon I started getting errors while starting the computer. The errors are: "Changelcon MFC Application has stopped working", "persistence Module has stopped working", "an error had occured while starting c:\program files(x86)\intel\bluetooth\btmshellexe.dll".

I really need your help guys, I have no idea what to do and my finals are approching and I'm in need of sound on my computer so that I can watch lectures and tutorials... So please, help me somebody?

On a one week old PC? You didn't list what the PC is or any specs (Please fill in the "My System Specs") so we can't talk specifics of your PC.

A one week old PC with Linux and Windows on it (and who knows what all programs) could have corrupted it.

I would do a reinstall using the PC's restore (e.g. on a Dell they have a procedure to do a factory reinstall back to how it was when it was new). If you contact the PC vendor for warranty support, the first thing they are going to have you do is the factory reinstall, so you may as well do it. After you do the reinstall, hold off for a week or so to make sure everything works before delving in and changing things.

It's Asus zenbook ux31la.

That is a nice notebook. But, I would still do a factory reinstall, given the multiple problems.