When this situation occurs, there are three possible scenarios:
1. There is no fiber connected to the tester.
Ensure that the launch fiber is connected securely within the OTDR port
2. The fiber is too short for the tester to detect events after the dead zone.
Depending on the type of fiber tested, a fiber under test (beyond the launch fiber) may be too short.
3. There is a bad connector or broken fiber within a few meters/feet of the tester.
To test for this, use a Visual Fault Locator such as VisiFault to see if there are any breaks or a bad connector.
Inspect the end face with a fiber microscope such as the Fluke Networks FT600 FiberInspector Pro.
In addition, try another launch fiber.