Maybe it's just me and my own experience, but anytime my Volvo won't start I always check the fuel pump relay first. It can tell me if I have power to the fuel pump and also if I have a ignition signal to the coil. It's located over the front passengers knees, under the felt panel. If you hold it in your hand while cranking, you should feel it click when it powers up. If it does, it tells you that you have a (required) signal from the ignition. This mostly rules out any problem with the primary side (power to coil) of the ignition system. This is the same (negative) signal that causes the coil to fire and at the same time holds the relay closed and maintains power to the fuel pump. If it clicks, the fuel pumps should run and the coil should fire. Try this during a no start condition and post back.
steve