Can't connect after doing a "reboot"

I am using a Beaglebone for 4 months now and never had this problem. I flushed it and installed the new OS (the latest one debian 7.9), then I connect to it with

ssh root@

that works the first time, when I do

shutdown -h now unplug it and replug it again it works.

But when I do


it reboots but I can’t connect or ping it anymore. Once I unplug and replug it in, it works again.

Any ideas?