I have a 02 Lexus LX 470, cranks but wont start, had a mechanic look at it, he couldn't find out the issue, he brings an electrician, and he says the key is no good, but the key has worked since, I got the truck, could this be the problem why it wouldn't start.

 

That's definitely a puzzling situation. While it's possible that the key could be causing the problem, it seems odd that it would suddenly stop working after all this time. It might be worth getting a second opinion just to be sure. There could be other underlying issues causing the starting problem. Good luck getting it sorted out!