One thing that is recommended by all of the major video softwares, is that you have two separate hard drives for video work (important for capture and for encoding). The reason for this, is that your hard drive has to keep switching back and forth, between reading from the software what to do, and at the same time, try writing your video to the hard drive. While this can work successfully, the best method is to have two hard drives. One for software, and one for data. One thing that might help, would be to shut down all non-essential tasks on your system and try again.