Please does anyone have idea of what could make my toyota avesis 1998 model hatchback not to start?

I have tried some technicians. Some said the fault is as a result of bad ECU while others are suspecting the cranksfta sensor. i have chaned the crankshahft sensor before now with a fairley used one when i experienced similar problem and it was solved. now they are saying the brain box is burnt and need replacement. the brainbox they have brought so far could not resolve the problem. maybe they require decoding and all that.

please any help from car electric gurus in the house? i will be most grateful.

@Poster
I wish you had tried another Crankshaft sensor before having them touch the brainbox in the first place. BUT if they replaced the original ECU back the way it was and you were there to supervise the whole thing, then I will suggest you try another crankshaft sensor.

This is why its very good to buy at least 2 or 3 of those sensors once one solves a problem with them. I just hope they replaced the ECU exactly the way it was without stealing or misplacing anything there.