SQL Statement For Combo Box

I have a query, called Building Query. it has 5 columns.

Building
EquipmentLocation
PartName
Category
PartNumber

I have created a form, with these five as comboboxes. I want each to reference the one before it, so the user can select the part without error. This is somewhat complicated because each building has multiple locations, which in turn have multiple parts, which can be in mutiple categories, etc............
However, althought the selection process works it's not accurate. example:
say I select building 1. and location 1.2. The part name should be limited to "belt" and the category limited to "ef", thus limiting the part number to 5vx630. This is what happens instead:
I choose building 1, and then location 1.2. The part name is limited to "belt". The category gives me a full list of all four categories available in building 1. So then I choose the category "ef" (because I know what to choose) and am given the full list of all "EF" part numbers. So It seems to work fine until the last two selections. Perhaps you can help.

Name: cboBuilding
RowSource: SELECT Building.BuildingList FROM Building;
after update event procedure:
Private Sub cboBuilding_AfterUpdate()
Me!cboLocation.Requery
End Sub

Name: cboLocation
Rowsource: SELECT [Building Query].EquipmentLocation FROM [Building Query] Where BuildingList = cboBuilding
AfterUpdate Event Procedure:
Private Sub cboLocation_AfterUpdate()
Me!cboPartName.Requery
End Sub

Name: cboPartName
RowSource: SELECT [Building Query].[PartName] FROM [Building Query] Where EquipmentLocation = cboLocation
AfterUpdate Event Procedure:
Private Sub cboPartName_AfterUpdate()
Me!cboCategory.Requery
End Sub

Name: cboCategory
RowSource: SELECT [Building Query].[Categories_CategoryName] FROM [Building Query] Where PartName = cboPartName
AfterUpdateEventProcedure:
Private Sub cboCategory_AfterUpdate()
Me!cboPartNumber.Requery
End Sub

Name: cboPartNumber
RowSource: SELECT [Building Query].PartNumber FROM [Building Query] Where Categories_CategoryName = cboCategory
AfterUpdateEventProcedure:
Private Sub cboPartNumber_AfterUpdate()
Me!Productssubform.Requery
End Sub
(this is to requery the subform the then displays the part number, the number in stock, and the number needed to be at full changeout level) This also isn't working all of a sudden

Can anyone help me???? It must be simple but I've read every thread in here about combo boxes and SQL's and just can't figure it out myself.