The phone randomly turns off and restarts itself. I thought it was due to the battery but even when its not over-heated,...

You might have to buy a new battery for it.

Through research, I've discovered that your not alone and that this is a problem most owners of this device have. You should probably go to the samsung website itself and ask them about it (the link below). I would also recommend looking at a dissembly of the device to find out what makes it's wifi tick, because it may just be an issue with the PCB antenna. http://www.samsung.com/us/support/servic...

Did you try charging it back up? If your unable to recharge it than try using another charger or buy a new battery for it.