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The pilot light is lit, the thermostats are up as high as they go, you have power and the boiler is cold.

A quick overview, You have all of your thermostats turned up as high as they will go. You have 120 ac volts power or you are assuming you have power for now.
Your pilot light is lit.
Your gas control knob or dial is turned to the on position and your boiler is cold.
A number of things can cause a boiler with power and a lit pilot light to not fire. This is not in order of likelihood, just a list of possibilities.
1Your thermostat is defective.
2 Your 24 volt transformer is defective.
3 Your zone valve end switch or switches are defective or the wires from them are loose.
4 A spill switch has tripped.

5 A roll out switch has burned out
6 Your gas control valve is defective.
7 Your vent damper is not opening or it's end switch is not showing that it is opened.
8 A low water cut off is showing low water and preventing the boiler from firing.
9 A secondary aquastat is defective.
10 Your primary aquastat is defective.
11 Your relay is not pulling in. or is defective.

The above list shows the most common possible causes for your problem. Many older boilers do not have spill switches, vent dampers, roll out switches, low water cut offs or secondary aquastats.

This alone is a good reason to replace your boiler.
Please notice the images below click on the image or text below to see instructions on how to test to see if that is causing your problem.

PLEASE don't go changing parts randomly in hopes you will solve the problem by chance, if this is too hard for you please stop and let me help you with the 24/7 Help Line.

Your Thermostat Transformer and Relay Honeywell Zone Valve end switch Taco Zone Valve End Switch
Spill Switch reset button Spill Switch Location Fusible Roll Out Switch Gas Control Valve
Vent Damper Low Water Cut Off Secondary Aquastat Primary Aquastat.