Can't see pictures or videos from phone on sd card.

[speedyjr]

For some reason on my note 2 whenever i transfer pictures or videos on to my phone when i go to the gallery it shows a picture of a lock and says cannot view them but when i plug my phone up to the computer i can see them just fine. why is it doing this all of a sudden and what do i need to do. my last option is resetting my phone and reformatting my sd card.