Just a FYI... when you need to add an edit, just use the Edit button located in the lower RH corner of your posts. First, there's no such thing as BIOS drivers. Second, without knowing which driverset you installed or where you downloaded them from, the latest official nForce4 driverset v6.86 is available from nVidia here...
http://www.nvidia.com/object/nforce_nf4_archive.html