Does it makes the "Clicking" noise when you try to start the car? If yes it could be starter. Some time bad starter could cause such problem. If your radio and lights are working, i guess battery is ok. Just replace the starter and you would be good to go.
All the best :-)
Have you changed the spark plugs? If no, please do.If necessary please replace them. Also check your filters like Air filter and fuel filter. Only clean air filter can increase the mileage of the vehicle by 10%. If the problem continues, please have your vehicle inspected by your professional...