To complement Devilin Carnet's advice. On my 2110 there are the following few codes and setups involved:
WEP Security Key: This is located on a sticker attached underneath the 2110 base unit.
When you first connect to broadband you have to start your internet browser and type into the address box: voyager.home (or 192.168.1.1)
The BT Voyager 2110 Configuration Manager screen will open.
You need to then enter the Broadband account User Name and Password that have been supplied by your Broadband ISP ADSL service provider. (This is nothing to do with the 2110 itself. Is this what you are missing?)
Then click connect and it should work.
If you have to get into the advanced settings of the Configuration Manager then you click on the word advanced on the left hand side of the configuration screen and then if prompted for access security details you enter:
User Name admin
Password admin
(This is the only instance of needing a username or password for the 2110 or it's setup/management that I know of.)
If it is working perfectly via the wired connection is it possible that the wireless end is not set up properly? eg the laptop or the computer with the wireless adapter on.
Good luck.
ps Is the wireless light on the front of the 2110 blinking or off. If it is off then it might be worth looking under the advanced section of the configuration manager screen as there is an option to enable/disable the wireless feature.
pps if you want to reset your 2110 back to factory default settings just to clear out any electrical cobwebs etc.
Turn on the 2110
locate the reset pin hole at the back of the 2110
insert a paper clip to press the button inside
keep the button pressed for 5 seconds until the power light switches on. The 2110 will reboot.
Restart the computer.