this happen to me and turned out to be corrosion on battery terminal, clean them very good.
Does the engine crank but not start? Or does it not even crank? Based on the information you gave, you could have a bad starter or weak battery. Dead battery. Recharge it or get a new one.
Bad starter or fualty battery connections. Check all grounds and/or bring the starter to autozone to have it checked
Remove the battery and take it to a car parts store (kragen, etc) and have them test your battery. The process is quick and should be complimentary.
If the engine does not even crank, it is battery or starter related. Check all connections and the charge of the battery itself.If it does crank, it can be 25 additional reasons why engine does not start.
The amperage required to turn over or crank most automobile engines is between 70 and 140 amperes. At 12 volts this works out to be 840 watts to 1680 watts of power for a few seconds from the battery.
If you know the battery is good, then you have a bad ignition switch or starter, or a loose wire.
There may be a problem with the relay on the ignition switch. There may also be a problem with the battery it may be have enough juice to run the light and radio but not enough to turn over the engine.
it works in side the battery
A 12 volt battery with about 600 cold cranking amps works well. A little bigger if you live in a cold climate.
Double check that the battery works, then check if the engine works.
how does a battery work
1. Disconnect the battery ground cable. 2. Disconnect the battery positive cable. 3. Remove the battery positive cable nut from the accessory wiring junction block. 4. Remove the battery cable from the starter motor BAT terminal. On the 2002 Venture, The positive battery terminal also supplies power to the circuit breaker and relay assembly located at the left corner of the engine compartment right over the battery. The battery cable for this vehicle is a "factory only" replacement part and is very expensive, in the neighborhood of $130.00 and tax. A perfectly satisfactory alternative is to use a generic battery cable of the right length connected from the battery to the starter motor, and a generic battery cable with ring terminals on both ends connected from the starter motor back to the circuit breaker/relay box. This alternative is an exact electrical equivalent of the factory part, works great, and saves a bunch of both time (ordering part) and money. Good luck!