HTC One reboots after the last splash screen, any solution?

Hi guys,

I have an HTC One device which I've been using since August '13. Few weeks back I somehow got my phone not responding. In the beginning, it would slow down, and just let me open the setting view and then suddenly shows a dialog with a message "... not responding" (with a 'wait' and 'ok' options to choose from).

After giving it a restart for a few times, hoping that it would eventually work, thing went worse than I expected. My phone would now automatically reboot itself and this reboot happens after the last splash screen with a white background and "htc One" text appears. This is a continuous loop which only stops when the battery is dead.

I took my phone to a mobile phone lab and they told me that you don't have an option besides having to change your motherboard (which costs around 400$ - including shipping charges I guess). I took my phone to HTC official distributor here and the guy listened to the problem and asked me to change the motherboard. This is worse than I could ever imagine!!

FYI, my brother brought this phone for me last year. He got this phone with an ATnT contract which he's still using. I had it unlocked here in Pakistan which means although I have an option to claim the device (as it's still in warranty) but as I've already unlocked it, there doesn't seem to be a way to have it claimed.

Please tell me what's the best solution for me? I'll be truly grateful.

Thanks,

Umar.