Thank you Robin. I believe I have made a very small amount of progress. However, now the MOSFET (switching a motor) starts up and just continues running.. 
I've attached my code that I have tried my best with.
It makes perfect sense now what you are all saying.
#include <dht.h>
#define dht_apin A0 // Analog Pin sensor is connected to
int ledPin = 13;
int MOSFETPin = 8; // choose the pin for the MOSFET
int pirPin = 2; // PIR input pin (for PIR sensor)
int pirState = LOW; // we start, assuming no motion detected
int pir = 0; // variable for reading the pin status
int micPin=7; // microphone input pin
boolean value =0;
int tempPin=A0; // Temperature input pin
boolean val =0;
dht DHT;
void setup() {
pinMode (ledPin, OUTPUT);
pinMode(MOSFETPin, OUTPUT); // declare MOTOR as output
pinMode(pirPin, INPUT); // declare PIR sensor as input
pinMode(micPin, INPUT); // declare microphone input
pinMode(tempPin, INPUT);
Serial.begin(9600);
delay(500); //Delay to let system boot
Serial.println("DHT11 Humidity & temperature Sensor\n\n");
delay(1000); //Wait before accessing Sensor
Serial.begin(9600);
}
void loop(){
// Start of PIR sensor
pir = digitalRead(pirPin); // read input value
if (pir == HIGH) { // check if the input is HIGH
digitalWrite(MOSFETPin, HIGH); // turn motor on
delay (5000); // leave running for 5 seconds
digitalWrite(MOSFETPin, LOW); // turn motor off
if (pirState == LOW) {
// we have just turned on
Serial.println("Motion detected!");
// We only want to print on the output change, not state
pirState = HIGH;
}
} else {
digitalWrite(MOSFETPin, LOW); // turn LED OFF
if (pirState == HIGH){
// we have just turned of
Serial.println("Motion ended!");
// We only want to print on the output change, not state
pirState = LOW;
}
}
// Start of Mic program
value =digitalRead(micPin);
Serial.println (value);
// when the sensor detects a signal above the threshold value, LED flashes
if (value==HIGH) {
digitalWrite(MOSFETPin, HIGH);
delay (5000);
digitalWrite(MOSFETPin, LOW);
}
else {
digitalWrite(MOSFETPin, LOW);
//Start of Temp Program
val =digitalRead(tempPin);
Serial.println (val);
// when the sensor detects a signal above the threshold value, LED flashes
if (val==HIGH) {
digitalWrite(ledPin, HIGH);
}
else {
digitalWrite(ledPin, LOW);
}
DHT.read11(dht_apin);
Serial.print("Current humidity = ");
Serial.print(DHT.humidity);
Serial.print("% ");
Serial.print("temperature = ");
Serial.print(DHT.temperature);
Serial.println("C ");
delay(5000);//Wait 5 seconds before accessing sensor again.
//Fastest should be once every two seconds.
}
}