If H1 is empty, go to
With Worksheets("Sheet1").QueryTables.Add(Connection:= _
"URL;http://ichart.finance.yahoo.com/table.csv?s=" & _
Worksheets("Sheet1").Range("J1").Value & "&a=10&b=13&c=2011&d=06&e=6&f=2013&g=w&ignore=.xlsx" _
, Destination:=Worksheets("Sheet1").Range("$A$1"))
If not empty, go to
With Worksheets("Sheet1").QueryTables.Add(Connection:= _
"URL;http://ichart.finance.yahoo.com/table.csv?s=" & _
Worksheets("Sheet1").Range("J1").Value & "&a=10&b=13&c=2011&d=06&e=6&f=2013&g=m&ignore=.xlsx" _
, Destination:=Worksheets("Sheet1").Range("$A$1"))
Plse add code.

On Error Resume Next 
ThisWorkbook.Connections(1).Delete 
Err.Clear: On Error Goto 0 

With Worksheets("Sheet1").QueryTables.Add(Connection:= _ 
    "URL;http://ichart.finance.yahoo.com/table.csv?s=" & _ 
    Worksheets("Sheet1").Range("J1").Value & "&a=10&b=13&c=2011&d=06&e=6&f=2013&g=w&ignore=.xlsx" _ 
    , Destination:=Worksheets("Sheet1").Range("$A$1")) 

With Worksheets("Sheet1").QueryTables.Add(Connection:= _ 
    "URL;http://ichart.finance.yahoo.com/table.csv?s=" & _ 
    Worksheets("Sheet1").Range("J1").Value & "&a=10&b=13&c=2011&d=06&e=6&f=2013&g=m&ignore=.xlsx" _ 
    , Destination:=Worksheets("Sheet1").Range("$A$1"))