If the cells' row numbers correspond and the blanks you want to fill are truly blank then it could be as simple as:
Code:
'copying from Sheet1 to Sheet2 where sheet2 has true blank cells:
For Each cll In Sheets("Sheet2").Range("C3:C15").SpecialCells(xlCellTypeBlanks).Cells
Sheets("Sheet1").Range(cll.Address).Copy cll
'or
'cll.Value = Sheets("Sheet1").Range(cll.Address).Value
Next cll
This was between sheets in the
same workbook, so you'll need to qualify the workbooks as well.