Почему у вас вход KEYs, а присванивание идёт по KEY?
Какой сигнал идёт на вывод rst_n?
Что такое и откуда взялось LED[0]?
В общем, смотрите что нагенерил Матлаб для такой схемы:

Спойлер
Код:
`timescale 1 ns / 1 ns
module lab3
(
KEYs,
LED_0
);
input [3:0] KEYs;
output LED_0;
wire dtc1;
wire X1;
wire dtc1_1;
wire X2;
wire dtc1_2;
wire X3;
wire Logical_Operator3_out1;
wire X4;
wire Logical_Operator1_out1;
wire Logical_Operator5_out1;
wire Logical_Operator4_out1;
wire Logical_Operator6_out1;
wire Logical_Operator2_out1;
wire Logical_Operator7_out1;
wire Logical_Operator_out1;
assign dtc1 = KEYs[0];
assign X1 = dtc1;
assign dtc1_1 = KEYs[1];
assign X2 = dtc1_1;
assign dtc1_2 = KEYs[2];
assign X3 = dtc1_2;
assign Logical_Operator3_out1 = X3 & (X1 & X2);
assign X4 = KEYs[3];
assign Logical_Operator1_out1 = Logical_Operator3_out1 | X4;
assign Logical_Operator5_out1 = ~ Logical_Operator1_out1;
assign Logical_Operator4_out1 = X4 & (X3 & (X1 & X2));
assign Logical_Operator6_out1 = ~ Logical_Operator4_out1;
assign Logical_Operator2_out1 = X3 | X4;
assign Logical_Operator7_out1 = ~ Logical_Operator2_out1;
assign Logical_Operator_out1 = Logical_Operator7_out1 | (Logical_Operator6_out1 | (Logical_Operator5_out1 | X1));
assign LED_0 = Logical_Operator_out1;
endmodule