Hi .. If you have only one wire on the switch, then there is another wire that has broken away from the connection. or a wire has become disconnected. There needs to be two wires for the switch to function. Look inside the wall box and see if you can locate the other wire. Then use the two wires to connect to your new switch.

Switches always connect to hot (black) wires. In some cases you may find a white wire with the end taped black denoting it is serving as a hot (black) wire. Or you may find a white wire connected to the switch. If that's the case, the prior electrician did not properly mark the wire and it should be marked as a black wire. Wrap the end with black electrical tape after disconnecting.