Below are 3 simple commands that display how many users you have in AD, how many users that are enabled and also how many that are disabled.

Number of User Accounts
(get-aduser –filter ).count

Number of Enabled User Accounts
(get-aduser -filter *|where {$_.enabled -eq "True"}).count

Number of Disabled User Accounts
(get-aduser -filter *|where {$_.enabled -ne "False"}).count