Problem with Wordpress Image gallery, images not displaying

About 20% of my pictures are not displaying up after I upload them into the media gallery (they show the x and wont load the image page when clicked as well). They work fine on my previous website, however about 20% of the images that are uploaded to my new Wordpress website with the theme are not displaying. I tried uploading them multiple times, just for testing, but it doesnt help if that particular image is not working. Is there any good way to fix this or determine why they are not displaying?