Windows 7: clean install hd audio problem

Hi just wondering if any one has seen anything like this . upgraded a friends computer from xp to Windows 7 home edition computer is a asus main board intel cpu. after installing codecs and drivers using dvbdream (dvb tv software) the system sound works fine and the sound in dvbdream works fine on mpeg-2 audio and video but when watching h264 hd with ac3 sound there is video but no sound coreavc and cyberlink same thing. did two installs on that machine problem confirmed leaving frustrated went home to recreate the situation on my computer almost the same intel/asus combo and to my amazement audio works on h264 with ac3 same codecs.so now im sure its hardware related Windows 7 bug because xp on that machine has no issues.anybody able to point me in the right direction please? will removing and replacing the microsoft dtv-dvd audio decoder be any help or a waste of time? thanks

narrowed down the problem further still no fix seems Windows 7 won't do 5.1 thru the speaker jack only optical for ac-3. I do have the jack set for 5.1 in the options but still nothing latest realtek drivers as well.so the problem remains good system sounds work 5.1 test 2 channel speaker jack.just no audio on h264 with ac3.