Pedro, I want to thank you for the help and answers you have provided me, I'll republish a summary about almost everything I've done, things that I've explained before.
So far, these are all the options that I've tried.
1. Formating the entire External HDD: 1 partition FAT32
2. Formating the entire External HDD: 1 partition NTFS
3. Formating one partition to FAT32 and using that one (having two partitions)
4. Formating one partition to NTFS and using that one (having two partitions)
If I use Configurable USB Loader, the light on the HDD turns on for two seconds before loading the CFG screen, and then turns off, the CFG loads and get stuck. If I use WiiFlow, it only give the option to choose SD (which is inside the Wii U)
If I use my 8GB Flash Drive, it works perfectly on both (CFG and WiiFlow), it's a "Generic" 8GB Flash Drive (it's a Goku from DBZ flash drive)
I bought two flash drives on eBay (10 dollars per 128GB), and they have the capacity, and in fact, I transferred Zelda Skyward Sword only, just to give it a try, by using the Wii Backup Manager, and it worked, but when I tried to install the other games, it gave me multiple errors, and well, these two flash drives keep telling me that they are write protected, I've formated them to FAT32, NTFS, etc and it's the same (but as pedro says, I was told about this, because these are cheap generic flash drives)
If anyone might know the reason or a solution about it, or if needs to check the HDD by TeamViewer, I would really appreciate it.
Thank you.