Volvo Repair Questions? Ask a Mechanic for Answers ASAP
The cam sensor on a 2000 is different than the one on your 850. The cam sensor is a common problem on the 850, but it would cause it not to start, as it is only used during cranking if I remember correctly.
It sounds like you most likely have a problem with the fuel pump relay. The relay can get hot while driving and cut off. They are very common. I would recommend checking yours and replacing if it is original no matter what. Even if it isn't the problem, it will be eventually.
The relay is located under the cover for the fuse panel at the base of the windshield. Remove the four torx 25 screws and remove the panel. The relay is red and has "103" on it. Remove it and check the date code stamped on it. If it is original, I would replace it. You can find the relay here
Do you know how to pull codes with the A/B box behind the passenger headlight?
Put the jumper lead in A2 with the key on and press the button for one second. The red light will flash a series of three digit codes, if stored. For example, flash, flash, pause, flash, pause, flash, flash, flash, flash would be 2-1-4. Press the button after each code to go to the next one. Do the same on A6 and let me know what you find.