Please check the following items:

Fuel flow - To ensure sufficient fuel flow for ignition, confirm that the fuel pump is switched on and the mixture lever is set to rich (forward). Confirm positive fuel pressure prior to attempting an engine start. Refer to the procedures in the manual for more information.

Vapour lock - This can occur for up to approximately thirty minutes after the engine has been shutdown. After shutdown, fuel vapour can remain within the fuel lines as the result of high temperatures. This vapour disrupts the operation of the fuel system and creates an incompatible mix of air and fuel, so you might need a few attempts at starting the engine before ignition occurs.

Oil quantity - If you have engine management/failures enabled, make sure that you have sufficient engine oil before attempting to start the engine, otherwise engine failure may occur.

You can also start the engine using the power icon located on the 2D panel selector or the 'Ready for takeoff' option in the menu bar.