Move that jumper back to protect. Its for firmware loading.
What driver are you using in RSLinx? Are you using a USB to serial adapter? What comm port is it using?
The serial port on your SLC5/03 can be configured for DF1 ( default) DH485 or ASCII protocol, do you know how it is configured?
Do you have the offline file? If so take a look at how the port is configured.
If you can post the file here and someone can help you look. Zip the file first.