Please perform a printer self test by pressing and holding the  FEED button and switching on the printer.  It will print the current printer parameter settings. It may be that the baud rate setting of your printer is not correct.

The printer needs to be set to 9600 baud, which is the default setting. Please refer to the user manual.
 
The correct printer settings are:
Interface: RS232(EIA), USB
Baud rate: 9600
Data bit / Handshaking / Parity: 8 bit / RTS CTS / None
Language status: English
Printing font: 12 * 24
Printing density: Medium
Paper sensor setting: Medium
Black mark mode: Off
Cutter status: Without cutter
Printing direction: Normal
Command system: SPMP
Default codepage: CP437

v1801