Cannot upload photo into slider

Hi,

I don’t know when it started to happen but now I cannot upload or change photo in the sliders anymore.

Every time I clicked on the photo section of a slider, nothing responsed. It’s like when you click on a blank link.

This slider belong to the theme and not one of the plug in so I guess I have to ask you and hope that you might know the reason.

Please help me.

Thank you