Hi Lisa can you provide some more information
What is the model number and make of the rf modulator?
what wii output did you use to go into the rf modulator ?
what frequency does the rf modulator output at ?
What model number and make is the television ?
What type of cable is being used from the rf modulator to the tv ?
Is it a video cable or a proper 75 ohm impedance coaxial cable
what is the impedance of the rf modulator output is it 75 omhs and what is the impedance of the tv is it 75 ohms or is it 300 ohms if it is 300 ohms on the television ( usually antenna is a ribbon cable screwed onto the back of the tv rather than a coaxial socket ) different you need a balun
I am recommending your first point of problem trouble shooting first is to check the impedance of your television compared to the impedance of the rf modulator and compared to the impedance of the cable used. IF they do not match then power is lost and the signal won't get to the TV.