I had this exact same problem. I unpacked my Edison, snapped it into the mini-breakout board, connected two micro USB cables between the board and my PC, started up the terminal emulator, and ... all I saw was an endless loop in the boot loader. I could type one or two characters, but then it would freeze and eventually reboot.
mmi's note about the cables provided me a hint. I switched the ports on my PC from USB 2.0 to USB 3.0 ports. And just like that it booted up and is sitting at the Linux login prompt! So, if you are in this endless boot-loader loop, try changing the USB ports on your PC. Some ports may provide better/more power than others.