1994redaltimase

yeah, you read the title correctly. I took my car into the local Wal-Mart Tire and Lube on Saturday to get my oil changed as well as checking all the other lubes and air filter. The Friday before i had just driven over 100 miles from my college to home, and i have made this drive many times. When i drove it to the Wal-Mart everything was running perfectly fine. I left the car parked where they asked and went in to do some grocery shopping. After about 2 hours of waiting, i get called to the Tire and Lube center as they could not get my car to start. They (being teens of my own age) had used my trunk key to try to start the car. When I started it however, it was idling roughly between 300-600 rpm, and when i gave it gas it just sputtered and died. This had NEVER happend before i had taken my car there on Saturday. I've checked all possible wire connections for loose or possibly disconnected wires, pulled all 4 spark plugs, checked the air filter, and disconnected the battery to try to reset the computer. None of these things have fixed the problem. If you guys have ANY clue what i should try next, let me know, as i am clueless and dont want to spend several hundred dollars at a mechanic to find out its just a loose connection. Thanks.