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If you are using genuine archaic bipolar TTL parts, like a 7438 (with no letters after the "74") or other bipolar parts like 74LSxx, 74ALSxx, you must be aware that their inputs source current and will appear as a "High" or logic "1", unless pulled really hard to Ground.  The inputs must be pulled below 0.8 volts to appear as a "Low" or logic "0".  Since the inputs of a 7438 can source 1.6 mA, the required pull-down resistor is 500 Ohms or less - your 10K pull-downs are much to high a value to pull the inputs down to a "Low" level.

Traditionally, we would place a switch between the input pin and Ground, with a 5K or so pull-up resistor from the input pin to Vcc.

CMOS parts such as a 74HC38 (or most anything else with a "C" in the middle) have a very high input impedance, so a 10K pull-up or pull-down resistor will easily hold an input "High" or "Low".