No Sound on 40in LED Display through HDMI, works on old display

I have an AMD 5770 1Gb and I'm using the HDMI cable, with my old monitor I got sound, when I hooked up the new monitor, no sound. WHen I plug the XBox 360 into the HDMI, I get sound. Right click speaker in the bottom right, click playback devices, the AMD HDMI is checked as default, and has a green check by the little tv picture, but no sound, no sound lvls, also, it has my monitor listed as generic PnP in the device manager, not sure how to get it to recognize, or just send the volume and hope it works or what Need Sound though.