photoshop question

So I'll be working in photoshop fine for like, 30 minutes, and then when I try to cut/copy something and paste it somewhere it won't work. It'll just keep pasting the image I used before it. I've tried everything. ctrl +c, ctrl + x, edit -> cut, etc. Normally I just close and reopen photoshop, but that's such a hassle. Anybody know what's up?