Problem with my Asterisk server

i had installed asterisk 1.6 on RHEL 5. i had configured two snom 220 ip phones, two nortel i2002 and i2004 ip phones and many softphones. i had some problem with my server. i installed asterisk 1.6 on RHEL 5 on another pc. i copied the configuration files and overwrote them in the new pc. the problem is that the phones are not registering with the new pc. i had assigned it the ip of the old pc and the same ip is configured in the phones for the server. i have tried sip show peers but it does not pick up the phones. when i changed the ip of a snom 220 phone in sip.conf from host=dynamic to host= of the phone), then it worked with server. but i want to configured host=dynamic? how should i do that?

has it to do something with the mac address?

got that. that was a problem with the firewall. i just disabled it and everything worked fine.