I can't permanently delete or download files

Whenever I try to permanently delete a photo in my photo gallery, I get a message saying "Can't delete from device." I've tried deleting files by plugging my phone up to my computer, but the files keep coming back sometime later after they're deleted. Not only that, but I'm also unable to download images or apps. Whenever I try to download an image or app it says "Download Pending" even though I have 114 MB of space free. Is there a way to fix this?