Welcome back to our Community Forums! Thank you for getting in touch with us about this issue and I'm sorry to hear that you're having some mailbox issues.
In this situation, we would advise to run a Malware check on your devices to ensure there are no issues. After this, please reset your mailbox password, by clicking on the Forgotten Password option when about to sign in. Reset your password to something new and never used before and wait at least ten minutes before trying to access your mailbox.
Please give this a go and let us know how you get on. If you have any further issues, we will be more than happy to look into this further and help.