Do not install USBLoaderGX in priiloader, or you'll have issues with launching nintendont.
You need to install the forwarder channel, then in priiloader you install a boot.dol which loads the forwarder which in turns loads the loader.
priiloader>forwarder>Loader
if you do Priiloader>Loader, then it will not have AHB access unless you are suing Priiloader beta.
But in all cases, it's better to follow the forwarder's choice.
1. install the forwarder channel (TitleID : UNEO)
2. install the loader to SD (apps/usbloader_gx/boot.dol, icon.png and meta.xml)
3. download the "3-in-1 pack" from googlecode and go to /wad/dol/ folder, you will find a "forwarder.dol", this is the one you need to install in priiloader.
DIOS MIOS is shutting down if HDD init encounter an issue, so it can shutdown due to specific flashdrive or HDD.
Sometime, HDD are not always initiating the same way between two reboot.
I have a "Seagate free agent go" HDD, 1 time out of 3 it shutdown DIOS MIOS, 2/3 it works.
out of the working state, sometime it works, sometime it freeze because it didn't detect the partition.
Nintendont never had any issue detecting the drive and partition from my SD or USB.