I installed windows 7 yesterday .everything seems ok but mz speaker sound is not working.i went into sound ,playback.but thre it shows that high definition audio devise is not pluged in over speaker section.but everzthing was fantastic before installing win 7.also note i have external sound card on mz system.it doesnt seems to be drivers problem since in device manager-sound,video and game controller section it shows that this device is working properly. i dont know what to do .please help.