If you have installed the pre-amplifier properly and receive worse signal then before you installed it, one of the following issues may be the cause:
Over driving your tuner
If you have TV stations within 25 miles, it is possible to overdrive your TV Tuner with too much signal. Please see our article on choosing the correct pre-amp for more info. The symptoms of over driving will be a nearby channel with no reception, where as weaker stations may still come in.
Amp is not getting power
Device installed between the pre-amp and power supply, that do not state "Power passive" will block voltage, remove these items if needed. Even other amplifers installed between pre-amp and power supply can disrupt signal.
This can also be caused by using low quality cable, especially RG59 that does not have a solid copper conductor. Those cables cannot pass the voltage up to the amp over long runs. It is possible that a coax cable can be damaged, and still send a signal, but not pass voltage. Try replacing the cable between the pre-amp and power supply
Not getting FM
Many pre-amps have the ability to block out FM, through a feature called an FM Trap. This is often used when an FM Transmitters is within 10 or so miles, and is interfering with TV reception. FM Runs on a frequency between 6 and 7, and can affect nearby stations. To receive FM make sure to set the FM Trap to OUT.