[gokul]

Focusing on the limit switch problem:

1. It should be referred to as DigitalInput (1) or DigitalInput (4,1) - nothing else.
The first number refers to the slot where your digital module is - in this case Slot 4.

2. Make sure your switch itself is a normally Open type switch
Switches come as Normally Open and Normally Closed - closed will always show one unless it is operated in a different way.
You can check this using a multimeter.