My character will fall through the floor with this script:...

My character will fall through the floor with this script:

 {
     public float moveSpeed = 6.0f; // Movement speed
     public float turnSpeed = 90.0f; // Turning speed in degrees per second
     public float gravity = 10.0f; // Gravity acceleration
     public float jumpSpeed = 10.0f;
     public float jumpRange = 10.0f;
  
     float distGround;
     float lerpSpeed = 10.0f; // Smoothing speed
     float deltaGround = 0.2f; // Character is grounded up to the distance
     float vertSpeed = 0.0f; // The current speed of the Vertical Jump
  
     bool isGrounded;
     bool jumping = false; // Flag for jumping to the wall
  
     Vector3 surfaceNormal = new Vector3(1,2,3);
     Vector3 myNormal = Vector3.forward;
     Vector3 myForward;
  
     Ray ray;
     RaycastHit hit;
  
     Quaternion targetRot;
  
     // Use this for initialization
     void Start () 
     {
        myNormal = transform.up; // Normal starts as the up direction of the character
        rigidbody.freezeRotation = true; // Disables the rotation via physics
        distGround = collider.bounds.extents.y - collider.bounds.center.y; // Distance from transform.posistion to the ground
     }
  
     void FixedUpdate() 
     {
        rigidbody.AddForce (-gravity * rigidbody.mass * myNormal); // Apply constant weight force according to character normal
     }
  
     // Update is called once per frame
     void Update () 
     {
        // Jump Code - Jump to wall or simple Jump
        if (jumping) 
          return;
  
        if (Input.GetButtonDown ("Jump")) 
        { // If the player is pressing jump...
          ray = new Ray(transform.position, transform.forward);
             if (Physics.Raycast(ray, out hit, jumpRange)) 
          { // Checks to see if there is a wall
  
           //THERE IS NO METHOD FOR JUMPTOWALL!
           //JumpToWall(hit.point, hit.normal); // Yes Jump to the wall
          } 
        }
  
        else 
        {
          if(isGrounded) 
          { 
           //no; if grounded, jump up
           rigidbody.velocity += jumpSpeed * myNormal;
          }
        }
  
        // Movement Code - Turn left/right with Horizontal Axis
        transform.Rotate(0, Input.GetAxis ("Horizontal") * turnSpeed * Time.deltaTime, 0); // Update the surface noraml and isGrounded
        ray = new Ray(transform.position, -myNormal); // Cast a ray downwards
  
        if (Physics.Raycast(ray, out hit)) 
        {
          isGrounded = hit.distance <= distGround + deltaGround;
          surfaceNormal = hit.normal;
        } 
  
        else 
        {
          isGrounded = false;
          surfaceNormal = Vector3.up; // Assumes that the noraml is up to avoid some weird shit
        }
  
        myNormal = Vector3.Lerp(myNormal, surfaceNormal, lerpSpeed * Time.deltaTime);
        myForward = Vector3.Cross (transform.right, myNormal); // Finds the forwards direction with my normal
        targetRot = Quaternion.LookRotation (myForward, myNormal); // Alligns the character to the new myNormal whilst keep the same forward Direction
        transform.rotation = Quaternion.Lerp (transform.rotation, targetRot, lerpSpeed * Time.deltaTime);
        transform.Translate (0, 0, Input.GetAxis ("Vertical") * moveSpeed * Time.deltaTime);
     }
 }

I don't know why he is falling through the floor, I have tried adding rigidbody to the floor, a collider, making entirely new terrain, and moving the character upwards so that it will fall and have time to update and collide. Help please?