How can I make a script that plays an animation then requires you to press a key

Hello , I've been trying to make a Dance Dance Revolution clone where text pops up (in order to tell the the player what key to click(up,down,ETC) ).Now,the text popping up works fine.BUT I am unable to make a reliable way to check when the player clicks key.I think It may have something to do with the time given to the player to click,however this is a hypothesis. And furthermore I am unable to solve that problem either. Here is my code `

 public class Randomizer : MonoBehaviour {
     Animator anim;
     public bool death = false;
     public int i = 1;
     public int loop = 1;
 
     // Use this for initialization
     void Start () {
         anim = GetComponent<Animator> ();
 
 
         
     
     }
     
     // Update is called once per frame
     void FixedUpdate () {
         
         if (death == false) {//start1
             int oi = Random.Range (2, 4);
 
             if (oi == 3) {//start2
                 anim.SetBool ("Up", true);
                 anim.SetBool ("Down", false);
                 
             
 
     
 
                 if (Input.GetKeyDown (KeyCode.UpArrow)) {//start3
                     i = 3;
      }/*end3*/ else if (i != 3 && !Input.GetKeyDown (KeyCode.UpArrow)) {//start4
                     death = true;
                     
                 }//end4
 
  
 
     }/*end2*/else if (oi == 2) {//start5
                 anim.SetBool ("Down", true);
                 anim.SetBool ("Up", false);
                 if (Input.GetKeyDown (KeyCode.DownArrow)) {//start6
                     i = 3;
         }/*end6*/ else if (i != 3 && !Input.GetKeyDown (KeyCode.DownArrow)) {//start7
                     death = true;
 
                 }//end7
 
             
             }//end5
         }//end1
     }
 
     }

Please ignore the animation stuff as that is working fine .

Thank you for any help.