To troubleshoot please check the sign in to TalkTalk Mail here (webmail). Tell us if there's an error message or if you can sign in ok using the password. Compose and send the same mailbox a message and check that the message is in the Sent objects folder and in the Inbox. That's just to make sure the mailbox is working ok.
Tell us how you normally use your mail computer to read and send mail messages.
And what the part of the email address is after the @ for example, talktalk.net or lineone.net or tiscali.co.uk
And if you're just having problems signing in or getting a specific error message.
What breed IS your 'main computer' @annie24, is it also an Apple - iMac / MacBook - or something else; also, what application[s] are you using to access your email across all devises?
It could be a Mail synchronization problem!