Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Sorry to hear that you can no longer access your account. To better understand what happened, could you please share the exact error message you receive when trying to sign in at https://account.microsoft.com, preferably with a screenshot after hiding any personal information? Also, please confirm whether the account is a personal Microsoft account such as @outlook.com, @hotmail.com, @live.com, or an email address from another provider, and approximately when you last signed in successfully.
Please also share whether you recently changed the account alias, email address, password, or security information, and whether you received any Microsoft security notifications before losing access.