void __fastcall TForm1::Button1Click(TObject *Sender)
{
    OpenDialog1->Execute();
    int hFile= FileOpen(OpenDialog1->FileName.c_str(),fmOpenRead);
    unsigned int valor;
    unsigned int checksum=0;

    //Coloco el puntero en el primer byte a modificar
    FileSeek (hFile,0x10,0);

    for(int i=0;i<0x4BB0;i+=4){
        FileRead(hFile, &valor, 4);
        checksum += valor;
    }
     while(checksum > 0x100000000)
            checksum -= 0x100000000;
    AnsiString salida;
    salida=salida.IntToHex(checksum,8);
    while(salida.Length() < 8)
        salida = "0" + salida;
    FileClose(hFile);
}