I have a Alienware m17xR4 and when I reboot from Windows 7 into 12.04 I have no sound. The icon is there and all of the listed devices are still present just no sound. If I reboot in 12.04 back into 12.04 it stops working. If I reboot from 12.04 to Windows 7 the sound works fine in Windows. The only way to fix the problem with the sound in 12.04 in to shut the computer down for 15 seconds then start it again.
You should try to install the lastest drivers for your devices. If you didn't do it yet, follow the next steps:
I hope it works to you, and tell us soon if it worked OK!