Help needed: how do I contact a 2nd router connected to my main router?

[#1]

I have recently taken delivery of a spiffy new Plusnet Technicolor Gateway fibre-optic router with accompanying high speed access.  So far, so good.  My house is long and thin.  You can't have one wireless router cover the whole house.  I have a second (D-Link) wireless router that is connected to the main Plusnet router via ethernet cable down the other end of the house.  I have followed the D-Link instructions to set it up by connecting it directly to the computer (disconnected from the network).  This included giving it a fixed IP address so I can find it on the network and set up the wireless settings.  I've then reconnected the computer to the wired network, connected the D-Link router to the wired network at the other end of the house.  It seems to be working on the manufacturer's default settings (I can see the network on another device), but when I type in the address into the computer's browser, the network can't find the D-Link router.  The Help Desk say they can't (help, that is). 
How do I find the D-Link router and log in to it?  It's not on the Devices list on the Plusnet router admin page.  Is it something to do with fixed and variable IP addresses?
All useful suggestions gratefully received.
Thanks
Merlin3046

[#2]

OK folks, my mistake;  I didn't read the manual properly.  To see the router, you have to set your computer's IP address manually to a specific setting, after which it will work.  Apologies to the nice man on the help desk who was very patient and pointed out to me that it's a problem with the D-Link router, not the Plusnet one.  He didn't say, but no doubt thought, that it's clearly a wetware problem.
Merlin

[#3]

Have you also disabled DHCP in the second router?
You need to do that

[#4]

Without knowing the model number of your Dlink, I will guess it is probably 192.168.0.1
Try the following procedure to set up a simple wireless access point using your Dlink (or any other router):
Factory reset your Dlink router if necessary.
Do NOT wire it to the Plusnet router.
Use ethernet cable or wifi and connect to your Dlink router as normal.
Log into the Dlink at 192.168.0.1 using a web browser.
You need to make the following changes:
1. Disable DHCP server.
2. Change the IP address of the Dlink router to:
IP address:  192.168.1.220 (example)
gateway:  192.168.1.254 (optional)
dns:  192.168.1.254 (optional)
Save settings (you will lose connection to the Dlink at this point) and restart router.
Now connect one of the four 'LAN' ports from the Dlink router to your Plusnet router.  Do not use the WAN/internet port on the Dlink router.
Connect your wireless device to Plusnet router wifi, and confirm you can access the Dlink router at 192.168.1.220 using a web browser.
Next, connect the wireless device to the Dlink wifi, and confirm you can access the plusnter router at 192.168.1.254, and that you also have internet access.

The next step is to review and edit the wireless settings on both the Plusnet and Dlink router.