Router won't Change SSID

[#1]

Hi,
I have a Thomson 585v7 and it is frustrating the hell out of me! The support pages are useless too.
I'm trying to change the SSID of my network but as soon as it signs all my devices out of the network because of the change, it will not let me connect to the new network SSID. I have not changed the passkey so cannot understand why this is happening. I have tried searching but all I can find is stuff like "changing the SSID is easy". Well not in my case!
Any help would be much appreciated.
Thanks
James

[#2]

Some more info needed...  When you say that you can't connect to the new SSID you don't say whether the old one still works or you can't connect using wireless at all?  Also you say you haven't changed the passkey - Does that mean you've left it alone or entered the same one again?
Try (if you haven't) plugging a PC into a LAN port and using that for configuration.

[#3]

the "PlusnetWireless" SSID disappears and is replaced by the one I changed it to, so I can;t connect to the old SSID. I enter the WPA key that was in the wireless settings (and still the same as the one on the label on the back of my router) and none of my devices will connect to the new SSID. I did not change the WPA key in the settings at all, not even type over with the same WPA key.

[#4]

Ok, connecting via cable has sorted it. Thanks!