HC-SR04 sensor and I have a little problem

Hi, I'm using a HC-SR04 sensor and I have a little problem. The sensor is working well but when I put it in front of an object who is too far to be detected he stops sending ultrasonic waves even if I put it in front of a close object (50 cm for examples) after that, the arduino is always returning back 0cm :( :( until I unplug and replug it...

I tried to use the NewPing Library but the problem wasn't solved. I also bought 4 others HC-SR04 but nothing has changed.

If anyone has ideas to solve the problem, your suggestions will be most welcome. ;D ;D

I'm a french guy and I'm very sorry for my bad english :confused:

Thanks a lot Aymeric

I believe that it's better that you show your code, your schematic, IDE version and Arduino board.