1999 Hyundai Lantra runs and then wont start

the coolant temperature sensor is the better bet as to a problem sensor
however having the fault codes read at a professional service centre will save lots of money and time

Which engine, 2.7L?? Is it full of coolant?? If the water pump has failed, it a pretty expensive repair.

Iam sure you have a sensor problem here and it could the autochoke is flooding the engine as its not getting the right reading via the computer so check and change the temperature sensors before you start spending money on exotic causes like the computer

it could be you coil pack or the altanator

Have you checked your coolant level? Does the temperature gauge run in the red zone? IF the coolant is low refill with 50/50 mixture when engine is cool. Check for leaks on radiator and hoses running to and from the radiator . If the fluid is fine, watch the temperature guage. If it goes in to the red the thermostat/sensor may be bad and thinks it is over heating and will not let you start the car until it thinks its cool enough to do so. It will also do this when coolant is low.

First you have to determine if its fuel or fire. To check for fuel spray a few seconds of quick start into the air intake. If it starts and then stops. its likely a problem with fuel. If it doesn't start its likely spark or battery problems. Does it turn over?

sounds like a typical ignition coil break down. when they go bad they act up when they get hot. very easy to replace. it is what the plug wires come from.

could be ??the windings in the sensor have the insulation on the way out

you have an override toggle switch hidden somewhere under dash youll have to search for it.

sounds as though it has a blown head gasket.