If you let the inputs "Float", you will get very unpredictable outputs from your logic chips. THe inputs need to be either at logic "0" or logic "1", (+5V or GND). It's also not a good idea to try to pull the logic gate input to a logic "1" state through a resistor to a higher voltage, unless you have a way to limit the voltage (not the current, as you are doing here). Try setting your unused login inputs to gnd, then pull the one input to +5V through a small value resistor such a 100 ohm, the GATE output should follow correctly in an inverted fashion (Logic "0")...
Happy Switching!
Mad Soundman