This could be one or a combination of many things so try all of the below options. 1. CHECK THE EMULATION/CONTROL CODES OF THE PRINTER ARE SET THE SAME AS THE PC SYSTEM (IE. EPSON/IBM ETC)
2. CHECK THE SERIAL PORT (IF USED) SETTINGS ARE THE SAME ON BOTH THE PRINTER AND PC. STANDARD SETTINGS ARE 9600 BAUD, NO PARITY, 8 DATA BITS, 1 STOP BIT
3. CHECK THE HANDSHAKE (FLOW CONTROL) ARE SET THE SAME ON BOTH THE PRINTER AND PC (XON/XOFF ETC)
4. CHECK THE CORRECT CABLE IS BEING USED AS SOMTIMES THIS MAY CAUSE THIS PROBLEM
5. CHECK THE PARALLEL CABLE (IF USED) IS NOT LONGER THAN 2M (6FOOT) AS THIS MAY CAUSE DATA LOSS