Try to start Windows in safe mode with networking enabled. - Win10 http://windows.microsoft.com/en-us/windows-10/change-startup-settings-in-windows-10#v1h=tab01

Still in Windows safe mode, start Thunderbird in safe mode. - https://support.mozilla.org/en-US/kb/safe-mode

Does the problem go away?

As stated above, "I have uninstalled all virus software and tried in safe mode to no avail".

Indeed with networking enabled.

The problem persists.

Can you confirm you did start Windows in safe mode please?

Yes, I ran in safe mode with networking enabled and in safe mode without networking enabled and it opens and then goes straight to 'not responding'

What happens when you start Thunderbird in offline mode?

Same!

What is your account type - POP or IMAP? What's the size of your email archive?

All hotmail acounts so POP. Big email archive. But my previous (less powerful) laptop handled it and more.

I tried to disable sync, but I cannot get into the menu as it stops responding as soon as the program is started up.

Uninstall and install (even install of the latest downloaded program) results in all folders automatically appearing without setup so I haven't been able to remove accounts and try that.

I think this is the answer to your problem. http://thunderbirdtweaks.blogspot.com.au/2016/06/hotmail-proxy-errors.html

Chances are the culprit is your anti-virus software. Don't let it scan your Thunderbird profile folder. Don't let it scan incoming and outgoing messages. Don't let it scan attachments. Remove any anti-virus add-ons it may have installed in Thunderbird.

I uninstalled all virus software, disabled firewalls, it doesn't matter.

I have updated all Hotmail accounts so that they are all allowing POP downloads.

Having edited the POP settings online in the various Hotmail accounts, it gave me enough time the next startup to click on "offline" mode which allowed me to look around in the program without any problems. One of the servers was still set to the old Hotmail one, so I updated that manually (the others must have automatically updated).

Once I allowed the program to go online again and download messages it straight away stopped responding.

For good measure I have run it in compatibility mode for Windows 8 and administrator mode which made no difference.

Running a compatibility test comes up with the fact that the program is not compatible, though I am not surprised about that given it's not a Windows program.

Looking at the Mozilla update log, my problems coincide with their last update of the program (29/5), though I downloaded the latest version on 6/6 which is not working either.

So I uninstalled this extra little program Mozilla put on (some updater agent?) and the new Thunderbird.

I installed the old version of Thunderbird from a year ago which was thankfully still on my computer. Previously, this trick did not work, but I thought I'd give it another go, now that I have removed this little updater thingy.

Guess what? It works!

One account though, even though I changed the Pop server to IMAP, in account settings, it won't recognise it as a IMAP server and therefore doesn't seem to want to download. Is there any workaround for this?

I changed the Pop server to IMAP, in account settings,

You cannot change an existing account. See http://kb.mozillazine.org/Convert_a_POP_account_to_a_IMAP_account

If that worked the problem was about 99% probability your anti virus program. We see particular issues with Norton Avast and McAfee here simply refusing to work with new versions. But they are not alone, they are just the stand outs. for being pig products.

I am having this problem. I have done all the suggestions, including disabling lightening, allowing tbird through my firewall, etc, etc. And it WAS working fine til today. Not responding

What worked for me is locating the original download of the installer file from a year ago, and use that to re-install Thunderbird.

Plus, what people are saying about changing IMAP and POP servers for Hotmail is also true. Two of the accounts updated automatically, one didn't.

I learned over time that the problem was at Hotmail. See my blog post for how to fix it. http://thunderbirdtweaks.blogspot.com.au/2016/06/hotmail-proxy-errors.html

Eventually everyone using POP at Hotmail will be affected by this Microsoft Decision.

Don't use hotmail.

My problem was not caused by Hotmail, it was the updated version of Thunderbird. It stopped working when it installed the update.

I found in my download folder an old version of Thunderbird so I uninstalled the later version and ran the old installer. That fixed it.

GabyT said

My problem was not caused by Hotmail, it was the updated version of Thunderbird. It stopped working when it installed the update. I found in my download folder an old version of Thunderbird so I uninstalled the later version and ran the old installer. That fixed it.

I would really like to think it fixed your anti virus and it's blocking of the new version of Thunderbird it did not know. But I am sure you are right.

It has nothing to do with antivirus or firewall as I have removed all of it and reinstalled the new version, ran in safe mode, you name it.

All fixes suggested on the forums did not work, yet a simple re-installing of the 1 year old version did.

Checking the Thunderbird update log, my problems started exactly at the time of a Thunderbird update.

Bet you any money there was an update the other day, and that's why 'kaylaartist' has a problem now.