Not sure if anyone can help, but on July 4 I lost the keys to my 2008 Mitsubishi Eclipse, and I bought a new key. I had a locksmith use the key today and confirmed that the key works completely fine, but for some reason the engine cranks and doesn't start. The battery is fairly new and I haven't had any problems with the car before. It has about half a tank of gas and I haven't driven it since I lost the keys none days ago.

I'm having a mechanic check it tomorrow but I was curious if anyone has any ideas; I greatly appreciate any help.