Cant trim/extend videos with drag

Hello,

     Im trying to make a cinemagraph in Photoshop but I cant drag to extend clips by dragging them. Every time I try to cut a clip it covers my entire timeline with a preview of the video and doesn't work properly, however I can just use the cut tool for that so o big deal. But when i try to extend the beginning of a copy of that clip to overlap it just gives me what I had deleted in the previous steps. After searching very single video and forum I could find I have found that I am either he first person to encounter this problem or the first person to actually try and figure it out. Please help if you know!

Thank you!