Em suma, isso significa que a conta do PC está desativada.
The down arrow on the computer icon in Active Directory Users and Computers indicates that the computer account is currently disabled. Before this computer account can be used, it must be re-enabled. Resetting the account clears the password and allows the account to be used by a new computer. You must rejoin the domain after resetting the account. However, resetting the account will not work in this case until the computer is enabled
Fonte: link