Try this:
Select
Id,
Salt,
Password,
BannedEndDate,
(Select Count(*)
From LoginFails
Where username = '" + LoginModel.Username + "' And IP = '" + Request.ServerVariables["REMOTE_ADDR"] + "')
From Users
Where username = '" + LoginModel.Username + "'
And I recommend you strongly to use parameters in your query to avoid security risks with sql injection attacks!
Hope that helps!