Like it's out of gas. Take key out try again, sometimes starts?

Started having problems with starting. I was using a spare key. So stopped and started using the main key. The problem started again. Will not turn over. Like it's out of gas. Take key out try again, sometimes starts. Car gives me a digital reading that car is disabled. I don't know what's going on. After trying and trying it finally starts. It's really getting annoying. Once started car runs great, no sputtering, no stalling. I even had it on expressway, does great. Sometimes I don't drive for 2- or 3-days, the car is fine. It was cold this morning. Of course, didn't want to start. I went to an appt car and sat for about an hour. Of course, wouldn't start. After 5 minutes of trying to start it, it finally did. Drove home, stopped got gas, went back out for a bit. Tried to start little bit ago wouldn't start again. Help!