Arduino Leonardo disappearing suddenly

Hello! I received today the board and I power it up. Everything goes OK below the Arduino. I opened Arduino IDE, tried to select Arduino Leonardo and port...well it's one COM1 and sometimes "Arduino Leonardo COM5". Once I succeeded to upload the blink example and the led from board it's blinking but after that Arduino Leonardo disappeared from device manager and I can't reconnect. I've tried to reinstall the Arduino but nothing changes. At the boot I can see it on the list and sometimes upload a new code but suddenly after that is disappearing. What's wrong? Thank you!