If you have not used the email account either by logging in via webmail on a web browser or via an email client such as Windows Live Mail at some point within 90 days the account may be suspended. See link
If you have been able to log on previously it may be that there is just a problem with BT and you should not try and change anything and try logging on later.
Try using this link.
Access via Microsoft PCS will work as does access via browsers other than chrome. For some reason I don't know why, it seems Chrome is causing the problem. Maybe a recent update caused this, but I would assume BT will have to correct it?
Why would BT have to correct a problem with Chrome?
This has occurred since chrome on android was updated. BT have recognised the mail "app" on Android chrome is causing the issue and have accepted they need to resolve it.
I created a fault on 5th Sept which was closed on 11th Sept as "resolved" without explanation. I requested this fault be reopened yesterday as it is obviously not resolved but instead yet another new fault has been created (to maintain SLA's in fault resolution timescales in my view). I have been advised Level 2 will call me tomorrow to progress. Even clearing and resetting every Bt site settings under Chrome on all my Android devices does not resolve the issue. At least when Mail was under Yahoo the separate app worked as expected. Ever since this transition to Web mail by BT the service is not what I would define as one that is acceptable.
I am not aware of any SLA that applies to the Residential e-mail service. I believe that BT Business, who use Office 365, do have an SLA with Microsoft.
Gmail tends to be more reliable in my experience, so you may want to consider it. You can still use it to send and receive mail as if it comes from Yahoo or BT Mail.