The DVR5100 Hybrid Video recorder is not fully populated.
DVR5100 Series Hybrid video recorder: all versions
Disable camera channel where there is no camera connected to; prevent channel from showing in the recording schedule and sequence monitor screen.
If you have fewer cameras connected than your DVR5100 supports (for example, three cameras on an 4-channel DVR), disable the unused channels by clicking “Disable camera” in the General Cameras screen. See figure below. Disabled cameras are available in the General Cameras screen, and are removed from the Recording Schedule and Sequence Monitor setup screens.