It might be "lawnmower syndrome", where unburned fuel washes down the cylinder walls, reducing compression to the point where the engine won't start.

I have had this happen once with my 2000 V70-- it gave me a scare-- I thought perhaps my timing belt had broken. I pulled the timing belt cover and had a look, fearing the worst.

This problem is most often associated with running the car for a very brief period and shutting it off (moving the car in the driveway, moving it to the other side of the street), resulting in flooding. On a subsequent attempt to restart, it won't catch because of the compression loss, and it will turn over very easily because the starter doesn't have to fight compression, resulting in an abnormal cranking sound.

Try cranking it with the accelerator fully depressed. You can also pull the plugs and add some oil to each cylinder to restore compression.

Good luck!