Current is not coming to plug to start the engine

What make , model and year vehicle ? Engine size also . The brain box as you call it doesn't supply current to coils , just a ground . Check the coil with ohm meter .

try this link.
Car Won Start Copyright AA1CarYOU TRY TO START YOUR CAR BUT IT WON...
or this one.
Problem 5 Engine Cranks But won Start
or this one.
Troubleshooting Car That Won Start dummies

what is the VIN
what is true engine name, gas or diesel and size.
what country. (tells me fueling systems)
did you check all fuses, i bet you dont know how to really test glow plugs only the see a light glow is not going to work.
so are glow plugs really working, proper voltage at them and right current flow (a meter works here, amps , using amp clamp)
filters clean.
scan it?

my guess it does this only cold block. right. a key fact.
glow plugs failing
just because a lamp come on , dont mean much,
actual glow plug current is what matters. (proper)
only takes 3 things
proper compression.
glow plugs
fuel.

Have you checked the automatic shut down relay ?
It powers the injectors from a 20amp fuse number 5.

1 MAke sure the engine is turning over 2 Make sure the cam and crank sensors are plugged in 3 Make sure the fuel pump is coming on

You can have current reach the coil but if it is open or if there is an internal short it may also produce a weak or no spark at all. High voltage has to come out of there and it has to be distributed to the various plugs. You have more than one plug so check the distributor out also.

Have u checked my removing one plug, reattached the cable and tried to start. this will confirm whether current is coming in sufficiently to make it spark. If it does not spark then check the induction coil to verify that fuse is still OK and the induction coil is still working properly. If there is a short in the coil, no current will be passed on for the plugs to spark. The flooding will not occur if the engine starts(also check if the choke is not pulled or engaged).......................................sodeep

the plugs are givin current through the cam sensor

Your block heater is plugged into household current, and is not connected to the vehicle electrical system, so you can eliminate that as a potential source of the problem. You didn't say whether the check engine light comes on when the door is closed and you try to start the engine, but my guess would be a bad battery and/or charging system. Take the vehicle to Auto Zone, Advance Auto, Pep Boys, O'Reily's, or other retailer and have them test the battery. If you have a few bad cells, you will not have full starting current, which will cause the lights to dim. If the battery checks out, have them (or an alternator shop) check the output voltage on the alternator. It should be putting out somewhere between12 and 18 volts depending on the condition of the battery. Considering that you live far enough north to where you need to use a block heater, my money is on a bad battery.