2005 VOLVO S40 TURNS OVER BUT WONT START

Look down where the white circle is and you will see a black round casing with a 32mm (i think) nut on it. It helps to remove the air intake hose in front of the white circle for easier access.

turn the key on to position 1 preset miliage trip button anh hold for 2 second release and turn key to position 2 hold within 4 secods and hold til manitance info clears.

If there is a blinking car icon with an "X" over it. This icon means the Immobilizer has been activated and hence won't allow the car to start. It could be due to a bad SCU, Start Control Unit. The SCU is actually the ignition switch on these cars.
Most of the time it's triggered by the anti-theft system..You can try this trick i learned that the dealers won't tell you...try locking and unlocking of the doors five times with the remote to reset the immobilizer and see if this helps.
Good luck...i hope this helps...please take a minute to rate me a fixya.