My 850 had problems starting. Things got to the point where I could get the car started at all. The battery was replaced and all my problems were solved. The car ran like a dream for a while. However, the problem came back. The car had to go in anyway for its 80,000 mile service so I got them to have a look at this problem while they were at it. The garage (Volvo Dealership) left the car overnight and in the morning they couldn't get it started either. The engine would turn over strong enough but the engine would not start. They replaced the spark plugs and cleaned the distributor cap as part of the service and now the car starts just fine. Even on cold mornings the car starts fine now. Hopefully my problem won't come back.

If I was you I'd check the plugs to see that they're OK, clean the ditributor cap and make sure the battery has a good charge.

Hope some of this helps.