My player floats after going up a ramp and it doesnt go down.

This is what it looks like:

link text

This script from Brackeys Third-person video is perfect, except that the player cannot lie flat on the ground. I have a rigid body on my player but it still floats.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ThirdPersonMovement : MonoBehaviour
{
public CharacterController controller;
public Transform cam;

public float speed = 6f;

public float turnSmoothTime = 0.1f;

float turnSmoothVelocity;

// Update is called once per frame
void Update()
{
    float horizontal = Input.GetAxisRaw("Horizontal");
    float vertical = Input.GetAxisRaw("Vertical");
    Vector3 direction = new Vector3(horizontal, 0f, vertical).normalized;

    if (direction.magnitude >= 0.1f)
    {
        float targetAngle = Mathf.Atan2(direction.x, direction.z) * Mathf.Rad2Deg + cam.eulerAngles.y;
        float angle = Mathf.SmoothDampAngle(transform.eulerAngles.y, targetAngle, ref turnSmoothVelocity, turnSmoothTime);
        transform.rotation = Quaternion.Euler(0f, angle, 0f);

        Vector3 moveDir = Quaternion.Euler(0f, targetAngle, 0f) * Vector3.forward;
        controller.Move(moveDir.normalized * speed * Time.deltaTime);
    }
}

}

first there maybe a few things you may want to make sure of:
1-Have you freezed any position in rigidbody → constraints?
2-Is your rigidbody is kinematic, if it is uncheck it.
3-Your mass may be so low or your drag may be so high.
4-Is your Use Gravity box checked in rigidbody,if not check it.