are the plugged in via usb? and are you on windows 7? if so try this
1. Click start
2. Search 'manage audio devices'
3. Hit enter
4. look for your device.. should say something like...
Headphones
Turtle beach z11's
ready
click on them once then click set default at the bottom then click ok and you should be ok.
you should really buy some astro a40s tho :) gl