Is my iPhone dead after overheating?
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okay it all started when i had my iPhone plugged into the USB port of my laptop because my laptop was tethered to my 3G connection. i didn't notice that it was getting a bit hot, until eventually it gave me a pop-up saying something like "your iPhone has become hot. you can only use it once it has cooled down" or similar to that.
so i let it lie for a couple of hours until it was cool to the touch again. wouldn't turn on. figured the battery was drained. plugged it into the wall socket, let it charge for a bit, then it turned on by itself. to my surprise, it gave me the activation screen. okay, no biggie, i'll just reactivate then, fine. so i unplugged it (upon which it immediately died), and tried plugging it into my laptop. i guess the power from the laptop wasn't enough to keep it on, as it wouldn't stay on long enough to boot and be detected by iTunes. okay, so i'll plug it into the wall socket longer, i thought.
this is when i really started to worry. i noticed that it would intermittently reset while plugged into the wall socket. from the activation screen, it would search for a signal, not be able to latch on, and then reset. rinse and repeat. i started freaking out when it wouldn't even stay on but would just constantly repeatedly reboot over and over again. so on the activation screen, i pressed the little "i" icon above the "slide to unlock" bar. i'm not so sure what usually gets displayed there, but i assume it's something along the lines of the IMEI etc. well, pressing it would give me a blank pop-up.
alright, panic mode. last resort - unplugged the iPhone (immediately turned off), fired up iTunes, plugged it in. it's able to boot into recovery mode (good) and is detected by iTunes as a phone in recovery (good!). keeping fingers crossed, i attempt to restore it. no dice. i'm getting an error 21 on iTunes. tried it with a rebooted computer, multiple USB ports, and different cables. no go. error 21 each and every time, and when i unplug the iPhone, it immediately powers off.
finally, i replaced the battery (had a technician do it), but it's now stuck on recovery mode. updating via iTunes using a stock IPSW gets me an error 21. i'm using a stock USB cable that came with my iPhone. tried both in recover mode and in DFU mode. in DFU mode, it goes through the motions, then eventually restarts in recovery mode, and that's when it hits error 21.
tried different computer, different USB, fresh download of iOS6. still error 21. my phone's dead, isn't it?
i'm using a carrier-locked iPhone 4, never jailbroken.