try pulling the number two fuse (under the hood on the driver side)and reseating it. This is the fuel pump fuse. If that doesn't work try pulling the main engine fuse and reseating it. This works for me on my 95 850.

Test for spark (I just put coil wire near frame and hit starter). If you get spark then not cam sensor. If no spark then easy to replace sensor - although I found connecter a pain to reach.

If spark & fuel try grinding starter without letting up for a minute or even two without touching gas pedal. After about a minute you might get a cough, but keep going until really started.

Condition sort of Volvo version of flooding. I had this, went through plugs, cap, rotor, etc. Finally tried just grinding and slowly the cylinders caught - 1 then 2 then 3 and so on. Took about 1.5 minutes of grinding. No repeats since.

Good Luck!

Check the fuel filter. If not changed and you're at or near 100K miles, it needs to be replaced anyway. If it's really cold (below freezing), any condensation in the gas line could have had an effect too. Get it into a warmer than freezing garage for a few hours and see if it will start. Other than this, could also be the fuel pump. Hope the unit (position sensor) you bought fixes the problem, but if it doesn't, I'd check the places I mention here.

As an after-thought...these cars won't start unless they are in "P," or park. Sometimes the "park to neutral" switch (P&N) can go bad and even if it looks to be in "P" it's really not. Without the ignition on, hold down the brake and roll the gear shift from P to N and back very quickly about 20 times (a temporary solution to a failing component) and then shift back to "P" and see if this does the trick.
Good luck and let us know what the problem was.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.