Youtube and iTunes sound problem.

Alright then, we've definitely isolated it to your sound card, and not to any incompatible software like outdated Flash Players and Media Players.

The next step would to be display your list of sound devices in your Device Manager and open the one that says Realtek High Definition Audio (which would be your default audio device if I'm not mistaken)

(Head to Device Manager by pressing start orb --> type Device Manager ---> enter)

Select the Tab that says driver and please upload a screenshot like the one I've shown below from my own system using this tutorial:-

Screenshots and Files - Upload and Post in Seven Forums

Here is my screenshot:-

It looks like your drivers may be outdated.

Try to install the latest drivers for your sound card from this link.

Latest Realtek HD Audio Driver Version

Try unplugging all your devices from your audio ports, restart your computer with a Clean Boot and try plugging in your speakers/headphones again.

To perform a Clean Boot:-

Go to start ---> type msconfig ---> go to Startup tab --> disable all entries ---> Restart your computer

Also post a screenshot of your System Configuration from msconfig like the picture below:-

It's hidden at the bottom lol.

(MSE from Microsoft)

Before restart please.

EDIT:- Report back whether the unplugged problem still occurs after doing the Clean Boot