RAX80 and Synology ds120j NAS unable to connect

Going to give this a shot but making a few assumptions.

The orange light was on the RAX80 network port and not the Synology Network/LAN light (since the ds120j LAN light is either Green, flickering Green, or Off, no orange option).

A few things you'll need to help specify:

Is the Synology NAS set to use DHCP? Did you try powering off the NAS, plugging it into the RAX80, and then booting it up?

If NOT DHCP: Did you configure the Synology NAS to use an IP that's within the DHCP / IP scope configured on your RAX80? Is the IP a duplicate of another IP on your LAN/Network already?

Sounds lame, but are you using ports 4 and or 5 on the RAX80? Try using Ports 1,2, or 3. You may have Link Aggregation Enabled on the RAX80 or possibly a broken network config on the Synology (even though it has only 1 LAN port, if your synology was restored from a different model backup, it's unlikely but possible the NIC port is configured wrong).

Also just for kicks but do you have a different Ethernet / Cat 5e or Cat6 cable you could use instead?  

And you have rebooted your RAX80 correct?

Also helpful to understand your Synology DSM version, your RAX80 firmware version, assuming both are up to date...if not a great place to start...