sensorValue = analogRead(sensorPin);
What is getting stored in sensorValue? Why not print it, and find out?
if(sensorValue>100)
{
Is sensorValue greater than 100? How do you know?
else if(sensorValue<50)
{
Is sensorValue less than 50? How do you know?
else Serial.println("Fail!");
Why is a value between 50 and 100, inclusive, a fail?
AWOL - Take cough syrup.
How about you fix your code?