If the TV has composite ports and the NES has composite ports and you connect the RED to RED, WHITE to WHITE, YELLOW to YELLOW and set the TV input to the composite ports everything should work.
If it does not, then either the NES isn't transmitting, the cables are bad, or the TV isn't receiving.
To figure out which is a matter of substitution.
Connect to another TV. If it still does not work, then it probably isn't the TV.
Connect a different set of cables. If it still doesn't work, then it is probably your NES.