VBA to Multiply all numbers formatted as a currency by a cell value

I think you also need to fully identify the cell - [A1] refers to the activesheet, which may or may not have the correct value, and change the format as you change the value:

Sub CurrencyConvert2()
Dim theSheet As Worksheet
Dim c As Range
Dim dRate As Double

dRate = Worksheets("Sheet1").Range("A1").Value

For Each theSheet In ActiveWorkbook.Sheets
For Each c In theSheet.UsedRange
If Left(c.Text, 1) = "$" Then
c.Value = c.Value * dRate
c.NumberFormat = "[$€-x-euro2] #,##0.00"
End If
Next c
Next theSheet
End Sub

Sorry - I forgot to wrap my code in tags, and now I cannot edit it.....