Does the furnace have power?
If you can switch the supply fan on or hear an ignitor sparking or clicking or any other activity in the furnace, then the furnace should has power.
Look for an inspection window on the face of the furnace. Do you see red or green or amber LED lights? If there is nothing then the switch might be off or breaker has tripped.
Code requires an On/Off service switch for furnaces and boilers which may look light a normal light switch located near the furnace. Look up in the ceiling area and towards the entrance of the furnace room. It should be labelled or have a red cover plate but often same as every other switch in the house.
If the switch and breaker are on, there is one more switch on the fan door of the furnace. If the door off or loose then the contact switch may be open.
If there are still no signs of life, then the power will need to be tested at the furnace. The thermostat wire connections may be easier to access and the low voltage at R & C should be 24 volts. If you have control power then the furnace has power.
Furnace is trying to light but fails
A fan is running and will not shut off but no heat.