Are the phones plugged in directly to the 7100 or are they going through a connected PoE switch?
Telnet to the 7100 and run the following debugs:
Debug ip ftp-server
Debug ip dhcp server
If not plugged in directly, then plug the phone in directly. When the phone is booting up, you will see a cancel button, press it and then enter 4,6,8,* to default the phone, then when prompted for passcode enter 456. The phone will then boot up.
Copy the debug to a text file and then attach it to your reply.