Your storage shelf was ordered with NBU 5220 or separate? Also make sure you intilize the storage completely, check the control panel to make sure it is completely up and then only turn on the appliance.
Also as per the admin guide can you check the two labels
"When you order a NetBackup 5220 and a Symantec Storage Shelf together, these
units are initialized together at the factory to create a matched pair. Matched
pairs provide optimum performance and they should always be used together to
help ensure successful installation and configuration.
To help you identify matched pairs, check the labels on the back of each Symantec
Storage Shelf. Each unit has two labels that identify the serial numbers of the
matched pair."
Also at what level it gives you error while loading? Can you put the screen shot here. If you read the loading procedure it will tell exactly what is the reason it is not loading?