I have a mustang 2000 v6. One day my car decided not to start up anymore. At first it made a grinding sound, figured it was the starter. I'm a college student so I didn't have the resources to fix it at the time, I took the battery off and let it sit there for a good week or so. My parents came to visit me and my father wanted to fix the car, turns out since I hadn't had my car in a while I lost the key. We called a locksmith to make a new key. After he made the key we tried it on the car just to show my father the problem with the car and what do you know the car magically turned on. Parents left home thinking it was just the chip in the battery, I did too. Day later I drove the car to the gas station and when I was leaving it decided not to turn on anymore, and I was using a new key. Now it doesn't even make a grinding noise. I get on the car and everything seems fine, lights are on, stereo turns on and everything. I turn the key and everything shuts off and the theft light blinks and makes a clicking noise. What could be the problem? Any help is greatly appreciated.