I am guessing you are still using the onboard sound card? if so... when was the last time that you updated the Realtek HD sound drivers
? Can you tell us what version you have?
Also, corrupt video drivers can cause some form of freezing, I suggest you uninstall your video driver
, along with the PhysX drivers, download a fresh copy of the latest Nvidia drivers for your OS and install it again.
Also, make sure you are not having a Heat Problem... another cause of freezes.
I would also leave the 9600GT installed, it is a good video card to have if just to handle your PhysX side of things... it will use the same drivers as your GTX so there is no problems or conflicts there.