I've had my powerbot for almost a year. Just recently it would just shut off after I restarted it. Thought that it needed charging but still would shut itself off. Cleaned everything out including the brush, turned it off for a minute and turned the power button back on. Pushed the start button and it would do a circle and then power off. Did this a couple of times and it still powered off. Any suggestions of what to do or what's wrong?