Rigidbody Addforce Not Working

I Have The Following Script For a Simple Rigidbody Movement, but When I Press Keyboard Keys It Doesn't Move At All. Keep In Mind That I Didn't Change Any Of Rigidbody's Settings. Code:

 public class CharacterMovement : MonoBehaviour
 {
     bool IsForward, IsRight, IsLeft, IsBackward;
     Rigidbody rb;
     public float MoveSpeed = 10;
     void Awake()
     {
         rb = GetComponent<Rigidbody>();
     }
     void Update()
     {
         if (Input.GetKey(KeyCode.A))
             IsLeft = true;
         if (Input.GetKey(KeyCode.S))
             IsBackward = true;
         if (Input.GetKey(KeyCode.D))
             IsRight = true;
         if (Input.GetKey(KeyCode.W))
             IsForward = true;
     }
     void FixedUpdate()
     {
         if (IsLeft)
         {
             rb.AddForce(-transform.right * MoveSpeed * Time.deltaTime);
             IsLeft = false;
         }
         if (IsBackward)
         {
             rb.AddForce(-transform.forward * MoveSpeed * Time.deltaTime);
             IsBackward = false;
         }
         if (IsRight)
         {
             rb.AddForce(transform.right * MoveSpeed * Time.deltaTime);
             IsRight = false;
         }
         if (IsForward)
         {
             rb.AddForce(transform.forward * MoveSpeed * Time.deltaTime);
             IsForward = false;
         }
     }
 }