Captures won't transfer to usb. And after trimming a video, the preview option does not work.

i have formatted my usb twice. When i transfer my captures its not there. The app on Xbox that shows all usbs keeps saying i need to sign in, even though I already am. After trimming a video id click the preview option, but it's all blank. It will play the whole video, just not when i trim. Only way i can see it is when i save it

:)