just installed a wdc wd6400 aaks-75a7b2 sat 640gb on a asus m4n78 pro motherboard running windows 7 but it only shows 101gb what would cause this


What capacity do you see on the BIOS? Also if you check Disk Management do you see any unallocated space?

have you updated the bios to the latest version?  there might be a drive size limitation on the bios.  did you set the bios to read the drive correctly?