It sounds like the printer itself is not on the network, so when trying to reinstall the software it searches, but can't find the printer. Can you enter your network settings directly on the printer itself using these steps:
Select Network Settings
Select Wireless LAN Setup
Select Setup Wizard
. A list of all available SSIDs appears on the LCD screen. The SSID = The name of the network.
Select your SSID from the list. Note
The product will display all wireless networks available by the order of their signal strength, and your SSID will probably be listed at the top of the list. The SSID name is XXXXX XXXXX the router or access point, and the default name is XXXXX XXXXX brand name of the router or access point.
If your SSID is not listed, your router or access point may be set to not broadcast its network name. Please stop here and let me know, otherwise continue:
If your wireless network has security enabled, enter your network password, then press Start
A message appears indicating if the connection was successful as well as asking if you want want to print a network connection report.
to print the report
From the report, you should see an IP address
listed, please post that here
source: epson.com nx420 technical faq