You need to provide more details to debug this issue. Can you open a bug in https://bugs.launchpad.net/neutron/ and upload the Neutron service logs (server, agents, etc). Did the stack process finish correctly? Do you have connectivity from the computer running the dashboard to the server?
I installed openstack on Ubuntu using devstack and after running "./stack.sh" I tried to log in the dashboard and I got the error "Connection to neutron failed"