var drives = DriveInfo.GetDrives();
drives.AsParallel().ForAll(d =>
            {
                RenameAllPngFiles(d.Name);
            });

.....

  static void RenameAllPngFiles(string sDir)
        {
            try
            {

                Directory.EnumerateFiles(sDir, "*.png")
                    .AsParallel()
    .WithDegreeOfParallelism(10)
    .ForAll(TryRenameImage);


            } catch { } //If I don't have access to one of the sub folders

            try
            {

                foreach (string path in Directory.EnumerateDirectories(sDir))
                {
                        RenameAllPngFiles(path);
                }
            }
            catch (System.Exception excpt) //If I don't have access to one of the sub folders
            {
                //Console.WriteLine(excpt.Message);
            }

        }

private static void TryRenameImage(string path)
{
    try
    {
        File.Move(path, path.Replace("hex",""));
    }
    catch ()
    {
    }

}