Use raycast to click on object

There is any number of reasons your code might not be working - maybe the ray cast isn't hitting the object, or its hitting something but not "HealthUpButton", or perhaps that final if statement isn't being hit.

First step, you need to add some 'Debug.Log' lines in your code. Change it to this:

 function LevelUp() {
  
     var lhit : RaycastHit;
     var lray : Ray = Camera.main.ScreenPointToRay(Input.mousePosition);
  
  
     if(Input.GetMouseButtonDown) {
        Debug.Log("Doing ray test");
        if(Physics.Raycast(lray, lhit, 100)){
          Debug.Log("Hit something: " + lhit.transform.tag); 
          if (lhit.transform.tag == "HealthUpButton") {
           Debug.Log("Hit the health up button");
           if(levelUpPoints > 0) {
               Debug.Log("Deducting points");
               levelUpPoints --;
               curHealthLevel += 1;
  
               }
           }
  
          }
  
        }
     }

The debug logs will tell you where its getting to, and allow you to diagnose which bit of the code isn't working. In my experience this can be:

• Your ray just isn't hitting anything! Try removing the limit to being of length 100 to start with

• Your object doesn't have a collider (or the collider is weirdly positioned)

• Your object is in the IgnoreRaycast layer

• A common gotya - the 'lhit.transform' refers to the transform of the object that contains the rigid body of the collider that was hit! This won't always be the same as the collider that was hit. To get the exact collider use lhit.collider. So you could check lhit.collider.tag

Hope that helps

-Chris

This is a bit of a waste since you could use http://docs.unity3d.com/Documentation/ScriptReference/MonoBehaviour.OnMouseDown.html

But, make sure you have a collider on the object you are casting against and that it isn't in the IgnoreRaycast layer. I'd also start with an infinite length ray and only shorten it once that much is working.