I have this mobile phone which I bought from a ultra Mobile agent. Once in a while the battery goes dead, and despite charging it again 100%, I still cannot seem to power on. I have tried everything like removing the covers, the battery, waiting a minute then reinserting it again, then pressing the power again, but the power still does not come up. I usually have to remove the casing as i think the tight fit casing was blocking the control buttons, but still this does not help. Can the gurus please suggest a fix. Thank u.