That sounds like your BeagleBone (the controlling computer responsible for running cgminer and lighthttpd, and all network I/O) isn't turning on. To be sure - are you unable to see a device show up on your DHCP list provided by your router? The MAC address might be identified as a Texas Instruments device if you use nmap to scan the network. The more information you provide, the better your results from this forum will be.