control panel, admin tools, disk management
look and see if a partition on the data disk is marked as bootable or "active". if it is that may be the problem. \
Make sure you have a backup of your video files first, in case something happens to the partition.
You should be able to change it to "not active' if it is showing up as activehttp://www.sevenforums.com/tutorials/197157-partition-mark-inactive.html