usually, people have the reversed problem : all working, except Metroid!
How did you manage to have all other game not working?
First, let's update the loader to be sure you are using the latest revision :
USBLoaderGX 3.0 r1214
extract the boot.dol file located in the /IOS249/ folder, and place it on your SD card in /apps/usbloader_gx/boot.dol
and launch the loader from the Homebrew channel is you don't have the forwarder channel.
secondly, you need to have the correct custom IOS too.
do you have d2x cIOS v10 ? you need a base 56 in slot 249 and base 57 in slot 250
then:
- Check that your USBloaderGX is correctly using slot249 as default IOS
- Check that your games ISO are correct (use a program to verify the ISO, like Wit/wwt or WiiBackupManager Sha1 option)