Insure that there is not a splitter in the cable line between the preamplifier and the preamplifier power supply.
Insure you have properly installed the preamplifier per the instructions.
You cannot have any standard splitters or an amplifier, in the line between the Preamp Output and the power inserter "TO AMP" port. They would block he voltage from getting to the preamp.
Try replacing the cable between the preamplifier and the power supply.
Verify that a preamplifier is needed by visiting www. antennaweb. org.