I was using my phone normally about 2 days ago, then put it back into my loose shirt pocket. When I took it out a few minutes later, I realised that the phone was off. I turned it back on, and while it was on the "Samsung Galaxy S II" logo, I placed it back in my pocket to give it time to boot.
I kind forgot about it later, and when I took it out about half an hour later, I realised it was still on the same screen. Thinking that my phone has frozen, I tried to depress the power button for about 5-10 to shut it off, to no avail. I did a battery pull, replaced the battery but found that I was unable to boot the phone at all.
Thinking that maybe the battery is flat, I tried another 2 more original Samsung batteries that I had with me, both fully charged. Nothing worked. I even tried entering recovery and download modes to no avail. I also tried several other methods described in XDA including plugging in the battery while doing the keypress for download mode, both volume buttons while without a battery and sticking in a connected USB cable, and even my old USB jig. Nothing. No boot screen, nothing on the capacity buttons.
Oddly though, if I plugged in my battery and press and hold the power button for 5 seconds, then leave the phone aside for a while, I noticed that it gets warmer. If I pull the battery out, it cools down. So it seems like turning on the power does "something", but the phone wouldn't boot. Plugging it into to computer doesn't recognise it either. Neither can Odin 3 see it.
Is my phone truly dead? Or is there any possibility of fixing it?