serial communication hung up

matlab is getting hung up(not responsive) as there will be no '>>' in command prompt and there will not be serial transmission of data . the i am trying to implement is :

s = serial('COM3');
set(s,'BaudRate',9600,'StopBits',1);
set(s,'Parity','none');
fopen(s);
fprintf(s,'W');

but after this matlab gets hung up ????