A good first step is to reset the camera to its factory/default settings. A changed setting can sometimes cause odd behavior that looks like a card or playback problem, and a full reset is a simple way to rule that out before assuming hardware failure.

Since you've already tried different memory cards and batteries, resetting the D7000 is the most practical next troubleshooting step based on the information given. If the issue continues after a reset, that would point more toward a hardware fault and the camera should be checked before using it for important paid work.