I am not a hardware person, but if you are using the switch box (RF) that came with the 130XE, you would need to be able to connect the old connectors to a current coax connection. If you have done this, I would check that the channel switch matches the channel number on your TV.
The simplest solution (though it would cost money) is to buy a composite monitor cable for the 130XE. I know Best Electronics sells them (http://www.best-electronics-ca.com
) along with other resellers. For 8-bit hardware support, I would recommend AtariAge (http://www.atariage.com/forums
). Most Atari-Forum users are 16-bit Atarians.