2005 Chevy Malibu pass key

I am having trouble starting my car. A month ago I had it towed and service, they told me then it was the fuel sending unti in the gas tank, $1k repair. Now 3 weeks later, it won't start again, turns over, but not getting gas, just like before. I had it towed again.....but they call me the next day and say it started fine for them. But they tell me, my key is an after market key, not the original from Chevy. I bought the car from my mother and this is the key she had for it, been using this same key for 2 years, and no, no tramsponder in it, nor a resistor. And it worked for two years....
Now I don't believe the car had a problem with the gas sending until at all, I think it was the start of this current problem.......suggestions please