Check your remote. It may have a button on it that says cable/tv or something similar....like antennae or whatever. If that doesn't work, look on the vcr/dvd player itself. There may be a button on the front that you can push that will set it back to antennae. You can also look on your tv itself, and there may be a little button to push to set it to an antennae, rather than cable.
Also, do you know if, as Rob asked, anyone else you know is having the same trouble? If they are, then the trouble isn't with your tv or dvd/vcr.