Hi,
Pressing “Windows key + Q” opens the Search charm to search everywhere or within an open app (if the app supports app search). Windows Store on Windows 8.1 has its own search function there is no need to use shortcut key.
I would suggest you to use Music app to search using Windows key + Q and check if it works. You may also refer this Microsoft article:
How to search
**http://windows.microsoft.com/en-us/windows-8/search-apps-files-settings**
Hope this helps. If you need further assistance with Windows, let us know and will be glad to help.