The S40 is a compact vehicle from Volvo that has been in production since 1995 and is available in both sedan and wagon body styles. Early model S40 owners, like all owners of ageing vehicles, sometimes encounter engine-related issues as their cars age. There can be instances when the S40's engine cranks, but doesn't start. When this happens, there are simple diagnostic checks that can be performed to rule out the most common troubles.
Put the key in the S40's ignition and turn it all the way to the right without starting the vehicle. When the vehicle's electronics power up, listen for the fuel pump to engage. If no audible noise can be heard, the fuel pump may be bad.
Check the fuel tank to ensure that you have enough gas, even if the gauge indicates adequate levels. Being out of gas is a very common reason that an engine will crank but not start.
Pop the bonnet and inspect the timing belt, making sure it hasn't snapped.
Test each spark plug with a spark tester, replacing any faulty plugs.