Resources.Load texture problem

i want to make a pu system for my game and i want to desplay the icons of the power up and i've dont this

 public class PowerUpContainer : MonoBehaviour {
     public List<EBasePowerUp> PuList;
     public Dictionary<string,Texture> icons=new Dictionary<string, Texture>();
     
     // Use this for initialization
     void Start () {
         DirectoryInfo dir=    new System.IO.DirectoryInfo("Assets/Textures/pu/");
         FileInfo[] files= dir.GetFiles();
         foreach(FileInfo f in files){
             icons.Add(f.Name.Substring(0,f.Name.Length-4),(Texture)Resources.Load(f.FullName,typeof(Texture)));
             Debug.Log("Loaded texture : "+f.Name);
         }
     }
     
     // Update is called once per frame
     void OnGUI () {
         Texture icon;
         Rect r=new Rect(10,100,30,20);
         foreach(EBasePowerUp p in PuList){
             
             if(icons.ContainsKey(p.GetType().Name)){
                 icon=icons[p.GetType().Name];
                 //........
                 r.x+=r.width;
                 if(r.x>90){
                     r.x=10;
                     r.y+=20;
                 }
             }
         }
         
     }
 }

but i have a problem, the texuter loades with no error, my dicionary contains the key so the if(icons.ContainsKey(p.GetType().Name)) is true... but the key value is null and i can't find the problem, the texture is loade without any error and is null... i have tryed to display all the textures that are in the dictionary and all are null... i think the problem is with "Resources.Load" but i'm a beginer in unity and i don't know so much