When you say it won't communicate, is it that you just can't see the PLC in RSLinx? If so then the driver is probably not set up correctly, which is the most common problem. Once you install the driver in your computer, and plugging in the cable, go to the Device Manager on your computer and see what comport it was assigned to. From RSLinx setup a RS-232 DF1 Devices driver make sure the comport that the computer assigned to the device is selected in the configuration window. Aslo in the COnfiguration window you need ot have the 1770-KF3/1747-KE device selected. Set your Error checking to CRC. I know that you definatly do not want to use the Auto Configuration. At this point click OK. All the rest of the defaults should be correct. You will then see the new driver listed. You can now close the Configure Drivers window. In the RSWho Window with the cable connected to the PLC and the computer, click on the new driver that you created and the PLC should show up. You can now access the PLC from RSLogix 500 or what ever software you might be using.