Hi! (Sorry for my english)
I had the same issue. I got it brand new (my wife’s gift) I remember that I charged my MS Band2 before batery run out… then the first time I forgot to charge it, it shut off, charged it, turned on, set date, and when I unplugged it, instantly turned off and didn’t turned on again when pressing the buttons. Then I connected the cable to my band and only appeared the black screen with batery icon and a little bar blinking at the corner of the screen. Never came back to set up screen.
Let it unplugged for five months and I charged again (now the battery was completely empty) and a few hours later (almost 12 hours) the band came back to life again. Set it up, weared it, didn’t let the batery go empty, but after one week I forgot to charged it again and the band shut off. Charged it, display turned on, set it up, but this time when I unplugged it the band shut off, like if the batery was empty. I get it plugged and try to factory reset it, but the device didn’t let me do that. So I gave up for at least 1 year and then I gave it a try once again. This time I was unable to get it turned on, the same batery icon and blinking bar in black screen. I let it connected almost 3 days and at last, the band came back to life (the day I’m posting this answer). This time I couldn’t set it up just the band alone, it asked me to pair it to my phone to complete the configuration process. So I did it, and everything went okay. Then I took the advice of you people and factory reset it, set it up, but before app-band configuration process, I ereased in the Microsoft app all the data and the previous MS Band2 device that was saved previously. So It detected a new device and finished the configuration. Now my band appeared to be okay. I’ll let you know how it worked in a few days.