I bought a Bu Vivo XL back in October. It's on its third trip back to Florida now, and the're going to replace it with a Studio Max rather than trying to repair it. I think that I've been without it for about six weeks over the past 4 months. They aren't very fast with turn-arounds.
However, relative to your problem, I had the same or a similar problem with mine. It would continuously re-boot and the only way I could stop it was to open it up and remove the battery. What I finally discovered myself (after it was returned to me after a "repair" for this problem) is that there wasn't eough clearance around the Power button and sometimes it would stick in, which would cause it to cycle between off and on and off and on . . . . I solved that by filing a little more clearance in the notch for the power button in the back of the case.
The replacement I'm getting doesn't have a removable battery, so I assume I won't be able to do the same fix if it develops the same problem. ;(