ihpone 4 shuts off randomly
I have an IPhone 4 that was given to me because the screen was broken, and had charging issues, I had my dad fix both the screen and the charge issue. it worked fine until I switched it from the original att sim to a straight talk sim. I didn't realize it was locked to att so it would turn itself off when I used the straight talk sim, I then fixed theat issue by plugging the phone ion waiting for iTunes to recognize it then unplugged it waited 20 seconds and plugged it back in. it recognized my phone then and unlocked it. About an hour later it began turning itself off randomly, and when I turn it back on it wont stay on until I plug it in and it is forced to stay on then I can unplug it until the next time it shut itself off. Also several hours later I plugged it into my pc and it says "USB device not recognized" and will only bring up iTunes on occasion.........please anyone who has even the slightest Idea of what might be wrong your advice will be appreciated!