Trying to conenct iPad to Router

[#1]

Hi,
My sister visited and wanted to connect her iPad to my PlusNet router to access the internet but couldn't get it to connect.
The iPad found the PlusNet wireless router but asked for the password to connect.
Now I have tried my Plusnet account password, Thomson (TG585 v7) Gateway password, the WEP code, and serial number from the bottom of the router but it wouldn't connect.
Since I only rarely use the wireless connection I thought it was the WEP code when I set up my laptop, but it's been such a long time I cannot recall.
Does anyone know which password the iPad is asking for?
I read in another thread while searching for help that you need to configure the iPad for a wireless connection to the router, and the default password is supplied on a card with the router (which wasn't in my case but that maybe because the router is old) or it's on the base of the router. But which one of all the numbers?
Thanks for any help.

[#2]

It will be asking for the wireless security key/password set in your router. Log in to your router and look at the wireless settings, the key should be case sensitive (unless security is set to WEP and is in HEX number format - that will work in whatever case).

[#3]

Maybe these will help:
http://www.plus.net/support/broadband/hardware/thomson_wireless.shtml
http://www.plus.net/images/support/broadband/hardware/thomson585/wifi-details.jpg

[#4]

Hi,
Thanks for the replies.
I was using the WPA-PSK Encryption Key but it still will not connect.
If I disable the Encryption I can sometimes connect and see the ipad in the Router admin page (WLAN: PlusnetWireless (1Mbps) Ipad), but I still cannot connect to the internet 
PS the ipad works O.K. on my sisters PlusNet wireless router but that is only about 12 months old.

[#5]

If you don't mind changing the wifi security setings, I'd sugest first setting both a new SSID and password but keep these both no more than 8 characters and see if you can then connect - if you dont have any incompatible devices it's also a good idea to set security to WPA2 only.

[#6]

Some older Plusnet routers had a problem with wireless connections to Apple devices if not running the latest firmware.  That was true of the Thomson TG585 v8, not sure about the v7. 

[#7]

Thanks for all your help.
I have finally got it to work