I know on my Windows 7 Pro 64Bit install with my Blue Yeti, I had to right click on the volume icon in the taskbar, lower right, click on Playback and make sure next to Speakers, that your actual speakers are listed and not the Blue Yeti. Somehow when I plugged my Yeti into the PC, after it was done its install and set-up, it had made microphone (the Blue Yeti) the default Speakers selected under the Playback tab.
Also check the Recording tab and make sure the Blue Yeti is shown next to Microphone.
Hope this helps some......