Okay, I foud the site and dowloaded the latest firmware update (even if it's from 2012). I have to download the kernel too? And then what's next? Should I format the SD, put the old firmware, update it and then try again installing YSmenu?
Backup.
Format the SD.
Install the latest firmware.
Copy the roms and save files back in the card.
Try to run the roms and see what happens.