It does go back to DHCP after a reset - you may not have held the button long enough, or the button itself may be defective.
There are a couple of different options open to you ...
First - you can set a temporary static ip address on your computer - let's say 192.168.0.2 and then attempt to find the DNS-323 and once you've done that change the address to one in the 192.168.2.x range
Or - you can use the Easy Search Utility which will find the DNS-323 regardless of it's ip address, provided it is on the same physical LAN - the probable reason why it's not working would be a software firewall or security suite. In most cases you have to tell the firewall (or security suite) that your home network is trusted, and if this is not done with the new network range then the firewall blocks the ESU from communicating.
Another way to deal with it is to reconfigure your new router to use the 192.168.0.x network range - essentially you change the router's LAN address to 192.168.0.x and it's DHCP range to match.