Try this one:
Select tblComputers.Computername, tblComputers.ComputerUnique,
tblComputers.Domain, Count(tblMonitor.MonitorID) As Total
From tblComputers Inner Join
tblMonitor On tblComputers.Computername = tblMonitor.Computername
Group By tblComputers.Computername, tblComputers.ComputerUnique,
tblComputers.Domain
Having Count(tblMonitor.MonitorID) > 1
Order By tblComputers.ComputerUnique