Thunderbird will prompt you for a password when it's needed. You may then tell Thunderbird to remember it, so that you won't need to type it again and again.

Thanks but I still cannot download my emails and Thunderbird has still not prompted me to insert a password have closed Thunderbird program and restarted up again but it has not solved my problem

If you don't get a password prompt, that usually means Thunderbird can't get to the server. In other words, it hasn't reached the point yet to prompt you for the password. Presumably you do have a network problem you'll need to resolve first.

I can connect to my network I have updated Thunderbird to 52.1.0 and still do not get a prompt to enter password and still cannot download emails did not have a problem until yesterday.

Try to start Windows in safe mode with networking enabled. - Win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode

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

Does the problem go away?

Have done as you suggested but still no prompt

Can you confirm you deleted the password Thunderbird had remembered previously?

Under Tools Options Passwords there are no previous passwords and under saved passwords there is nothing

There isn't much more I can suggest. Try to reboot your Router. If that doesn't help, you should probably talk to your email provider.

Thanks for the help but I still cannot download my emails and Thunderbird does not open window for me to insert password.

I ran Thunderbird in Safe Mode again and the window to insert my password opened and have been able to download my emails. Once again thanks for your help.

What Thunderbird extensions do you have installed?

Lightening but the problem has been solved when I ran Thunderbird in Safe Mode again