Set the 615 as an AP and its ip in the same subnet as the router it connects to. Router and the 615 must be connected via the WAN port.
Thanks for the quick answer, kukubau. Is there a config page in the 615 where you can just select AP? I did not notice that anywhere.
FWIW, I got the following to work...
1) Reset the 615 to factory defaults
2) connected my laptop to port 1, then
2.1) Configured wireless access with password
2.2) Disabled DHCP
2.3) Changed the router IP address to one 192.168.3.1 which I know was not an existing IP address
3) Disconnected my laptop, power-cycled the router.
4) Disconnected the wire going to the existing PC, reconnected it into Port 1.
5) Connected a new wire between Port 2 and the existing PC
That allowed the existing PC to work as before, and I was able to connect wirelessly to the router with my laptop and access the network like I wanted. The only thing I am not 100% comfortable with right now is accessing the router config via the IP address I gave it. Didn't need to or try that at this time.