Firstly check the user manual of the equipment you are trying to communicate with to make sure that the connector wiring is done correctly. Then collect information required to configure the serial port, valid commands and terminating characters. These are the information that you will need in your Labview vi. The attached link contains a Labview sample code for you to try out.
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=506500000008000000AE2F0000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0