|I assume these were laptops which were known to you. If so you could try powering the router off for about half a minute, then let it come up again (takes a couple of minutes). If that fails use the router reset button (usually a pin hole) and make sure you have your network name and wireless key handy.|
If they were unknown laptops then change your network password for something more robust (mixed letters and number, upper and lower case, up to 32 characters long).
Always pop back and let us know the outcome - thanks