Cannot Connect To Netcomm Wireless N Extender?

I recently just bought a Netcomm NP124 wireless extender as a computer on the other side of my house does not get within the range of my routers wireless.So i have opened the package and followed the step by step manual of how to set it up. it is as follows:

1. to initially set up the product we recommend you plug the NP124 into a power socket near both you existing router and computer (DONE successfully)

2. Plug the supplied Ethernet cable into your NP124 and connect the other end to the computer (DONE successfully)

*this is where the problem lies*

3. you can connect your devises through the web user interface. to open the web browser (internet explorer, Firefox, etc) and type 192.168.20.1 into the address bar and hit enter.

4. When prompted add in the username and password.

Before i keep going i must tell you that my desktop computer doesnt have wireless but my modem/router does so i connect my computer to my router via an ethernet cable.There are further steps but i cannot get past step 3. When i attempt to type the IP in the URL it says "problem loading page", "unable to connect". At all times my phone line is connected to my modem/router. These are the cable variations i have tried:

a) -ethernet from computer to NP124
-No ethernet connection from modem/router to computer
**this is the procedure outlines in the manual, does the manual assume i have a wireless connection
to the internet in my desktop?**

b) -ethernet from the computer to the modem/router
-ethernet from the NP 124 to the moder/router

c) now using an Ethernet hub:
-(ALL) NP124, modem/router and desktop connected to the hub at the same time

I cannot see why the IP does not connect, without this stage i cannot enter the wireless settings of the NP124. I have tested to see if other IP addresses work in the URL (eg the modems 192.168.1.1) and it works but the NP124 doesnt.