well, be sure all your fuses are intact, then dtermine if you have "fuel" and "fire" as David suggested.

For fuel, you should be able to hear the buzz from the pump when you turn the key, but before you crank it. You might need a friend to listen near the open gas cap - I'm told it's quite audible. There are some other simple tests in the FAQ's engine section, I'd follow those first. My 1990 745 had some mysterious problems that were traces to the RSR, but once it died and refuse to do anything when I turned the key. I had given up, called a tow truck, but the car decided to cooperate suddenly. I never figured out what caused it. I just got rid of the car.

You said you changed some parts out, als double and triple check to be sure you reconnected everything (esp. the coil wire).
--
Volvo #6: all wagons.... 1972 145S, 1976 245 DL, 1983 245 GL, 1986 740 GLE, 1990 740 GL, now a 1995 940...What's Next?