Been using BT mail fine for a year or more till early hours Mon 24th August, yesterday. Since then cannot log in to get emails, on my ipad, iphone, imac Windows 8.1 or Windows 7, tells me my use name or password for Btinternet is incorrect. It is not. If I try to log in via the server it tell me I have made too many attempts and to try again in 15 mins and that is the first time I try. I can only get them on my old Windows Vista PC??? What is going on? Something has obviously changed and it is not all my machines. They had problems with the link for email on BT.com the other day, one got taken back to the home page every time.
It would appear that there is some sort of glitch with the system if it is happening on all your devices except your Vista PC. I would not change any settings or passwords and leave things alone to see if it sorts its self out.