The phone needs to be flashed. However, the problem will continue. I have been having the same problem with my Blu Studio 5.5c D690U. I flashed the phone but exactly one week later, it stops working again. Stuck in start loop. What I was told by a Blu Store worker, is that there are a few Studios with Manufacturers' default. So, there is nothing you can do really, except buy a new phone or change the system software or board.
Good luck!