Just replaced the engine in a 2002 Focus. after finishing, I'm trying to start the car but it won't. The car was parked for 4 months before I bought it with broken engine. Can't get it to start. Does the car have any safety swithc, or security system? or anybody know where to go?

There is no safety switch beside the fuses and relays how did you replace an engine, did you rebuilt it from top to bottom or did you just put another used motor in? if you replace it with another motor assuming you did not mess with the timing such as the belt and the camshaft, check and make sure you getting fire from spark plugs, having a friend turn the engine over and you observing the plug. by pulling one wire with the plug and ground it and turn the engine over and see if you getting any sparks, second check and make sure you getting plenty of fuel to the fuel filter and the fuel pump is working properly. no fuel to the filter, check fuel pump, good pump, faulty crank sensor. that is the first two thing need to be check, fuel and sparks. if no sparks, check coil if its good and putting out 12V, if its not, check the cam sensor, may be faulty. faulty cam sensor will not make spark plugs fire. if you are getting sparks and fire, than it out of timing, rotate the distributor forward or backward with small movement no more than a tip of a car key at a time, when you capture the running or sputtering of the engine, movement should be no more the a pencil lead forward or backward. without using a timing gun the best way to know if you have the engine on correct but close timing if you able to crank/start the engine and it fire right up without keeping the key turn.