Polycom IP450

We have a few Polycom IP450s when I try to get them to register with the PBX (Asterisk 1.4.22-4) the 450s reboot in a circle and have a blank screen. The 321 and 550 work fine. I am new to the PBX world, not Linux or MS, just PBX. I am assuming it’s a config file issue, any help would be great.