It's impossible to access website - authorization prompt appears.
There may be several reasons of this issue. To determine them, the following conditions need to be checked:

1. There should be read + execute permissions for IUSR_ on the domain index page.

2. Root directory for the domains can be under Plesk protection.

3. Passwords for system user and IIS user can be out of synchronization.
1. Go to %plesk_vhosts%\\httpdocs directory and check permissions for IUSR_ account.

2. It can be checked using Plesk Control Panel. Go to Plesk, domains,, Protected URLs. If the root directory "/" is present there, it needs to be removed.

3. The password can be synchronized using the following command:

"%plesk_bin%\websrvmng.exe" --update-anon-password --domain-name=

Recommended buys!