There are a few possible reasons why photos might not be showing up in the iPhoto application:
Make sure that the photos are actually stored on your computer. If you have stored the photos on an external hard drive or cloud storage service, they may not be visible in iPhoto.
Check to see if the photos are in a supported file format. iPhoto supports a wide range of image file formats, including JPEG, TIFF, and PNG, but it does not support all file types.
Check to see if the photos are in the correct location. iPhoto looks for photos in the "Pictures" folder by default, but you can change the location in the application's preferences.
Make sure that you have granted iPhoto access to your photos. If you have recently changed the privacy settings on your computer, you may need to grant iPhoto access to your photos in the "Privacy" tab of the "Security & Privacy" system preferences.
Try repairing the iPhoto library. If none of the above solutions work, you may need to repair the iPhoto library. To do this, hold down the "Option" key while launching iPhoto, then choose "Repair" from the resulting menu.