Mitsubishi Repair: Check Engine Soon light stays on, mitsubishi montero sport, sonia sonia

Question
My 2000 Mitsubishi Montero Sport Limited just got it's oil change and right after that my "Check engine soon" light came on.  It drove but it was hesitating.  This morning I went to start it up and it start but wouldn't stay on and the check engine soon light, battery and oil light stayed on.  I gave it gas stayed on and was able to drive it. Could let me know what the problem could be and the cheapest way of fixing the problem.

I bought the car a year now and only did the oil changes so far.  Also at this oil change it was recommended that I change the air filter.  It was taken out but the repair man didn't have my type in stock so he put it back in.
Thanks for your help.
Sonia  

Answer
Sonia,
The place that did your oil change and attempted to replace the air filter may have failed to correctly reconnect the harness that plugs into the air filter box.  You can check this out yourself.  The air filter box is located near the front of the engine on the passanger side.  Look for any loose or disconnected wires around it.  Also, an air filter box that was not closed properly can also cause the problems you're experiencing.  If you can't see any problems or you don't feel comfortable doing this yourself, take your car back to the place you got your oil changed, and insist they fix this problem for free.  The problem was most likely caused by the mechanic anyway.
Good luck!