Not sure precisely what you're trying to do - when you move the mouse over
the rows, what are you expecting to happen, exactly...?

However, the following might give you a push in the right direction:

<asp:GridView ID="MyGridView" runat="server"
OnRowDataBound="MyGridView_RowDataBound" .......>
.......
</asp:GridView

protected void MyGridView_RowDataBound(object sender, GridViewRowEventArgs
e)
{
   if (e.Row.RowType == DataControlRowType.DataRow)
   {
       e.Row.Attributes.Add("onmouseover",
"this.style.backgroundColor=\"black\"");
   }
}

I'm sure you can adapt it for your specific requirements...