Why wont my 2000 F150 start?

just because the lights work doesn't mean you have enough power in the battery to start the truck. you might be able to jump start it, but turn everything else off-radio, heater, lights-they all take power away from the starter. if you can't jump it, pull the battery and take it to a parts store and have it checked and possibly charged.

Bad battery, probably. How old is your battery. 3.5 to 4 years is about all you're going to get out of one. The first cold snap should do it in.

you need 12.6 volts on battery.2.1 volts per say(each hole in battery.if you take a volt meter and check battery,red lead on pos.and black lead on neg. anything less than 12.4 volts is not good.if it starts,and it may then check battery again,should have 13-14 vdc.if battery is bad,you will soon see all guages on cluster panel sweep all the way to the right and the come back down to the left,then normal.if red battery light is on,most likely alternator is bad,most likely brushes shot on voltage regulator.if this is the case,you can get a regulator on ebay at a good price,i did and it fixed my motorcraft alternator.if this is the case,make sure to get correct one.i think they make a 95 amp and 130 amp.research your problem,dont throw $500.00-$1000.00 at it and it not be the problem.hope this helps.if pcm does not see correct voltage,it will not send signals to where they should be sent,and maybe give you incorrect false cel codes, if any.i have seen this many times.hope this helps.also you should not ever have to pump gas pedal.