Which version of Photoshop are you using and what is your operating system? Also, post a screen grab of the issue.
If you made a selection before copying, make sure that you are not copying part of a layer that is a smart object layer, a type layer, or a shape layer.
If you did not make a selection, and you are trying to copy or duplicate a layer, you can either right click on the layer and choose Duplicate or use the keyboard shortcut Control J (Windows) or Command J (Mac).
When you copy and paste in Photoshop, the pasted area is not offset as in most programs. It is pasted directly on top of the copied area. So there may be something on the pasted layer after all.
As Akash Sharma said, it would be helpful if you post a screen grab of the issue. The more information you provide the better others can help you.