Iphone 3GS-randomly no firmware

Today I had no signal on my phone in the middle of the suburbs when i picked my phone up i noticed the screen gave a little flicker and it did feel a bit hot.
So I turned it off for a few mins and then turned it back on.
when it turned on it prompted me to plug it into itunes and do a restore and would only do an emergency call.
So I did that 5 or 6 times and got a range of errors from 20000 to 1602
I have two usb cables - one is brand new and they both work on my itouch.
Ive tried reinstalling itunes on my main computer and downloaded a brand new version on my laptop - still not working.
Its a well looked after phone and its not even a hot day so overheating shouldnt be an issue.
any ideas what to do?
Iphone 3gs iPhone OS 3.1.3