Quick Fix -
Connect to the SH using the ethernet cable and turn WiFi on there - presumably you have a reason you need the WiFi from the other router ? I have a Linksys connected to SH2 in modem mode so I understand you might not want it.
Slower fix - use ethernet cable to connect to the router and see if WiFi enabled etc or do a factory reset and start again.
FYI you will probably have to reboot your laptop (or use DOS commands) to change networks/routers.
If you can't connect to the SH via cable try rebooting the laptop with cable connected to the SH.
To get to the SH config page it should be 192.168.0.1 in your browser and pw should be on the bottom of the router - default used to be changeme but not sure about SH3