Hi Perez,
Could you please help me to confirm the following information?
1. Has the configured global admin password been changed recently?
2. Make sure port 80 is opened in firewall.
At this point, you can also try the following steps to troubleshoot this issue:
1. Use a global administrator account defined in Office 365 that has the "onmicrosoft.com" UPN suffix.
2. Verify that the correct password is being used for the "onmicrosoft.com" global administrator account by attempting to logon as that account at: https://portal.microsoftonline.com/
3. Run through the Directory Synchronization Configuration Wizard supplying the user account with "onmicrosoft.com" UPN suffix and an enterprise admin account.
Thanks,
Mindy Pan