My S4 died yesterday. I took it out of my pocket to check the time and it was turned off. I tried turning it back on but it never got past the boot screen. 

It then stopped even turning on. I tried my battery in a mates phone and it worked. I tried his battery in my phone and it still wouldn't turn on.

After trying several different sequences of removing battery and pressing the home+vol up+power button I can finally get it to show the splash screen. When I attempt to go into recovery mode it also never gets past the splash screen.

I can get to odin mode, however it shows 
current binary: custom
Knox void warranty: 0x1

After googling what this means it looks like a counter has been tripped and voided my warranty (phone is 4mnths old). I have never attempted to flash a custom ROM, I haven't even updated from Android 4.3 that came stock on the device, can anyone advise how this counter could have been tripped? Am I basically screwed with warranty? should I now try and flash a custom rom to see if I can recover my phone?

Thanks for any advice.