If the props not turning at all check that Ctrl+E is still assigned to 'Engine Autostart'.
Or if you've been 'engines off-systems on', or were 'engine running-systems on', but alternator/generator off, you may have a low/dead battery. FS9 batteries are known for short life.
If prop turns but no-start, check that your mixture control (red handled knob or lever) is set to 'full rich' (ctrl+shft+F4).***Edit, but I see Gary beat me to it.

Dave
At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.