Here is the code that I'm running. Granted it's probably not the best way but I'm new at this and it works but when I add in the part about checking for the conditions to be complete (which aren't in here) then it doesn't work.
Private Sub txtPart_ID_Exit(Cancel As Integer)
If IsNull(Me.txtPart_ID) Then
DoCmd.RunMacro "mcrPartidok"
Else
If DLookup("stock_um", "tblParts", "ID = '" & Me.txtPart_ID & "'"

= "LN" Then
DoCmd.RunMacro "mcrLinInch"
Me.cckNoMaster = "off"
Else
If DLookup("stock_um", "tblParts", "ID = '" & Me.txtPart_ID & "'"

= "SQI" Then
DoCmd.RunMacro "mcrSqInch"
Me.cckNoMaster = "off"
Else
If Not (Me.txtPart_ID = DLookup("ID", "tblParts"

) Then
DoCmd.RunMacro "mcrNoPart"
End If
End If
End If
End If
End Sub