TG582n router requires constant logging in

[#1]

Thank you so much for your help and suggestions which are much appreciated. I will try everything tomorrow when I'm wide awake! Strangely we are also  having sound quality problems with our phones. I wonder if the two problems are connected?
Thank you again

[#2]

Undoubtedly, if your phone line is faulty it will mess up the broadband and probably cause dropped connections.
Start your own thread and we'll try and get you "guided through" to ultimately raising a fault.

[#3]

Quote from: RPM

Maybe your antivirus software is interfering with the login process? Some AVs can be obtrusive but best to check just in case and rule it out.

Using Microsoft Security Essentials with real-time scanning switched off. I tried to close the relevant process but wasn't able to for some reason. Can't imagine the programme just sitting in the taskbar would have an effect though.

Quote from: Anotherone

...check there isn't anything daft in your Firewall settings that might cause this.

Have Windows Firewall switched off as it's messed with sharing over my home LAN in the past.

Quote from: Anotherone

Do you have any customised settings? Have you tried the dreaded factory reset?

No custom setting that I can remember doing. I did change a router to use open DNS but that might have been on the router I had before this one.
Factory reset is the last resort which is looking more and more likely... 
Thanks for the ideas so far. Will try a factory reset later in the week when I've got a bit of time to set things up again and see if that fixes things.