Upgrading the firmware to sip88xx.11-7-1-17 fixed the problem for me. 

You might of ran into this bug: https://bst.cloudapps.cisco.com/bugsearch/bug/CSCuo92911/?referring_site=bugquickviewredir try factory restting it, follow these steps: https://supportforums.cisco.com/video/12504861/factory-reset-dx70-endpoint

you can download here: https://software.cisco.com/download/release.html?mdfid=286310330&flowid=80562&softwareid=280886992&release=1.9.17&relind=AVAILABLE&rellifecycle=&reltype=latest and for instructions: https://www.acano.com/publications/2013/08/A...

make sure the port is connected to is active/live. try manually setting the IP settings under IPv4 and try setting the tftp to point to call manager.