Why does this function time-out?

Although I clear COM4, it doesn't respond (although sometimes after reboot). I have included the code, and the output. What is my problem? (thanks)

=========== CODE ==========

function checkingCOM4_Callback(hObject, eventdata, handles)

            pause(.1000) %  <============================
                            disp('CLEAR COM4 PARAMETERS ')  
            pause(.1000) %  <============================
clc
delete(instrfind);
pause(0.1);
s = serial('COM4');
set(s,'BaudRate',9600,'DataBits', 8,...
    'Parity', 'none','StopBits', 1, ...
    'FlowControl', 'none','Terminator','CR/LF');
fopen(s);
s
fprintf(s,'g');
fclose(s);
delete(s);
clear s;

            pause(1)     %  <============================
                            disp('CHECK PORTS     (INSTRFIND) ')  
            pause(.5)    %  <============================

com_check = instrfind ;

if isempty(com_check)

    handles.com1 = serial('COM4')   ;

    set(handles.com1,'BaudRate',2400,'Terminator', ...
        '','DataBits',8,'Parity','none','StopBits',...
        1, 'Timeout',1)    ;

            pause(.1000) %  <============================
                            disp('OPEN COMM PORT  (FOPEN)')  
            pause(.1000) %  <============================

    fopen(handles.com1) ;

    i=0 ;

    while i<=5
        i=i+1   ;

            pause(.1000) %  <============================
                            disp('PING DEVICE     (FWRITE) ')  
            pause(.1000) %  <============================

        fwrite(handles.com1,[hex2dec('5A') hex2dec('A5')],'uint8')  ; 

            pause(.1000) %  <============================
                            disp('CHECK RESPONSE  (FREAD) ')  
            pause(.1000) %  <============================

        BoxGoStr = fread(handles.com1,2)    ;

            pause(.1000) %  <============================
                            disp('IF NO RESPONSE  (ISEMPTY)')  
            pause(.1000) %  <============================

        if ~isempty(BoxGoStr)

            pause(.1000) %  <============================
                            disp('CHECK BOXGOSTR (88,77)')  
            pause(.1000) %  <============================

            if BoxGoStr(1) == hex2dec('88') && BoxGoStr(2) == hex2dec('77')

                set(handles.ComAlarm, 'String', 'Coms Initiated', 'BackgroundColor', 'g');
                set(handles.CorrAlarm, 'String', 'Running', 'BackgroundColor', 'g');
                set(handles.CorAlarmTxt, 'ForegroundColor','k')

                pause(.1000) %  <============================
                                    disp('COM4 OPEN')  
                pause(.1000) %  <============================

                GoodComs=1;
                break

            else

                pause(.1000) %  <============================
                                    disp('COM4 FAILED    ')  
                pause(.1000) %  <============================

                GoodComs =0;
            end

        else

            pause(.1000) %  <============================
                                disp('COM4 FAILED') 
            pause(.1000) %  <============================

            GoodComs =0;
            break
        end
    end
else

    pause(.1000) %  <============================
                        disp('COM4 SUCCESSFUL') 
    pause(.1000) %  <============================
    GoodComs = 1;

end

========== OUTPUT =========

checkingCOM4 - output

   Serial Port Object : Serial-COM4

   Communication Settings 
      Port:                  COM4
      BaudRate:           9600
      Terminator:         'CR/LF'

   Communication State 
      Status:                 open
      RecordStatus:       off

   Read/Write State  
      TransferStatus:     idle
      BytesAvailable:      0
      ValuesReceived:    0
      ValuesSent:           0

CHECK PORTS (INSTRFIND) OPEN COMM PORT (FOPEN) PING DEVICE (FWRITE) CHECK RESPONSE (FREAD)

Warning: Unsuccessful read: The specified amount of data was not returned within the Timeout period.

IF NO RESPONSE (ISEMPTY) COM4 FAILED