Windows 7: Sounds not working properly

I recently reformatted my computer, before i can have 3 different youtube clips, a justin.tv stream on and i can hear every single page sounds.

After i reformatted, if i turn on a justin.tv stream and the sound is on, if i try to turn on a youtube clip, no sounds comes on. I have to turn off the stream, turn off google chrome, reopen up google chrome, and go back to the youtube clip before the sound works for youtube.
I do not know how to change the sound so that it does not prioritize and ignore like this, which is annoying, and if you can help me out i will be very greatful, i died too many times because i cannot hear the sound in website chatting games (epicmafia pings).
Windows 7 computer if necessary