Thanks for your reply Juanjo, I checked the 780ti in another system and it crashed as well, so got my Asus GTX780ti replaced with MSI GTX780ti and all is working fine.
Yes it was the GPU issue. Asus card was heating up too, the average temperature on Asus was 84C to 89C during rendering process, MSI has two extra fans on it so its temperature is approx. 67C to 70C while rendering
Thanks for the help