I want to design a counter in Verilog HDL which would have a press button when pressed the counter show start counting incrementally. However, the counter does not start counting. This is the major issue. What could possibly be wrong?

I have provide a code snippet below.

module pressbutton_counter(rst,clk,p_b,count);
input rst,clk;
input [1:0]p_b;
output reg [4:0]count;

always @(posedge clk)
begin
    if (rst)
       count <= 0;
    else if(p_b==2'b01)
       count<=count+1;
    else if(p_b==2'b10)
        count<=count+2;  
    else if(p_b==2'b11)
        count<=count+3;  
    else
        count<=count+1;     
end
endmodule