First and most obvious would be glow-plug. How's your ignitor? Does it have enough power? Take your plug out and see if it glows red, not just gets hot. If it doesn't, it's either your battery of your plug. If you have another plug you know to be good, check it with that battery. Just process of elimination. This is usually why they abruptly quit.
Don't change a whole lot of anything until you know this. If you have changed anything put it back to where it was. Try this, and get back to us.