There can be several reasons for being unable to login. The first step is to always make sure your login credentials are correct.
If you are looping in the login screen, or get an Access Denied error you can try these solutions:
1. Check that your internet browser is up to date
2. Clear your internet browser cache
3. On Windows 10, in the Options menu under Time & language settings change your preferred language to English
4. Go to the webpage https://portal.office.com/adminportal and navigate to the following page:
-> Azure Active Directory -> Enterprise Applications -> Nexetic Cloud Backup as Administrator -> Properties
From there, make sure that the "Enabled for users to sign-in?" option is turned ON