writingangel on "Image uploaded but not appearing on blog or under "Media Library""

I want to upload an image to "Media Library". However, once the image is uploaded, I cannot view the image on blog / under "Media Library" although it is clear that the image is uploaded. The image file is available in my /uploads file (FTP). Even when I upload the image through FTP transfer, it doesn't appear as well.
When I checked the link to the image file, it came back as error 404. What can I do to solve this problem? Thank you.