Files not found error

I just got a new Mac desktop. I’ve gotten Lightroom and photoshop all downloaded. I’m running into a problem when I try and upload my latest catalog into Lightroom. Lightroom can’t locate any of my photos. They all have the little “!” Error on them. When I go through the process of locating a photo, it says the file I’ve found has a different name than the original file, am I sure it’s the right one. I say yes, and then Lightroom greatly distorts my image. It gets stretched, flipped, and the colors are horrible. Why is this happening? I have never kept the original raw files so I don’t have those. But I’ve never had this problem before. Help!!