Does a browser refresh get you past the three animated dots? Recommended browsers are Chrome and Firefox but others may work.
The sign in usually works but if there's a delay of more than 6 seconds the mailbox Inbox doesn't load. This is caused by a delay, after the sign in, reading existing cookies, maybe a malformed cookie is present or there's a hold up by some other software you have running like an anti-virus scan or other browser add-on or extension.
Before you sign in, Select the Menu icon (triple line) top right and then Manage Cookies.
Then select Accept None and when the pop-up appears select Yes, proceed.
Then enter your email address and select Continue then clear the password box and enter the password then select Sign in.
All of the above is when browser cookies appear to be holding up the sign in to TalkTalk Mail. Subsequently you can select the Accept all option when the Privacy Manager next pops up.
If the sign in is still stalled then temporarily disable Internet security software that may be scanning and holding up the sign in and or re-launch the Internet browser with extensions or add-ons disabled to see if some software is stalling the appearance of the mailbox.