It could be a lot of different things. I would check the idle speed unless it's computer controlled. If the idle speed is computer controlled you can't adjust it and it probably isn't the problem anyway.
Check the throttle position sensor or the idle control motor
It should, unless you accidentally pressed "B"
More info needed, Carb or fuel injected????? Check TPS sensor in FI cars - common issue
Is your parking brake on?
You have to keep it down with your foot!
lack of fuel
did this just happen one day or was this an over time thing. did you replace something and then it happened?
Was it moving and they pressed the brake pedal to STILL the car? How do you KNOW it won't start?
The manual transmission has a starter interlock which prevents the engine from cranking unless the clutch pedal is depressed
You need a new battery. The same exact problem just happened to me in my 2002 jeep grand cherokee. The computer in the vehicle wont let it run unless it is getting a high amount of voltage from the battery. When you replace the battery, the problem should be fixed.
IT wont start cause on most cars when you press the pedal down the injectors will not spray out any more fuel that's why if your car is flooded people say to push the pedal to the floor
Sulfation can happen when battery is not fully charged and remains discharged