Volvo 850 Problem Report
Volvo 850 Engine Cranks Over and Doesn't Start
It's quite common for the the fuel pump to fail, causing a no start condition. The engine will crank over but it will not start.
To verify this the fuel pressure and electrical power to the fuel pump should be checked. If the pump is getting power and there's no pressure, replace the pump. If it isn't getting power, check the fuel pump relay circuit.