Changing Cell Background Color In Another Sheet Based On Cell Value

I am working on a workbook with 200+ sheets and an index linking to each of the sheets. On the sheets there is a cell containing the results of calculations and I need the cell referencing the sheet in the index to change background colors depending if the calculations value is greater or less than 0. I currently have working code that also changes the tab color of each sheet depending on the value, but i am trying to add the index cell background change functionality into that. also, the index listings is subject to change. my working code is

VB:

Private Sub Worksheet_Change(ByVal Target As Range)
If Range("d34").Value < 0 Then
Me.Tab.ColorIndex = 3
ElseIf Range("D34").Value > 0 Then
Me.Tab.ColorIndex = 4
Else

[Code]...

and the code i am trying to get working is

VB:

Private Sub Worksheet_Change(ByVal Target As Range)
Dim rngX As Range
Set myRange = Worksheets("Index").Range("A1:A500").Find(Range("C2").Text, lookat:=xlPart)
' the C2 is the reference the title that would be on the index
If Range("d40").Value < 0 Then

[Code]....

I keep getting the runtime error '1004: application-defined error or object-defined error the thing is, i ran the cell background changing code in a normal macro before integrating it in my other worksheet code first and it worked fine. I have a little code experience, though not much in vba and I am unsure what the issue is. if there is another better way to accomplish what I'm tring to do, that would also be fine.