PC doesn't detect my Leonardo any longer, only the bootloader

Hello!
After connecting my Leonardo to the PC, everything worked well. My board appeared in the device manager and I've been working with it for some time. Suddenly, I couldn't upload a new sketch and I saw that my PC stopped detecting the board and I can't find it in the device manager any longer. Only when I press the reset button the bootloader appears for some seconds in the device manager.
The lamps on the board are still turned on. I tried the board on another PC and with another USB cable but without results. I uninstalled and reinstalled the Arduino Software once again but nothing changed. There isn't anything plugged in.
Do you have any idea what else could I try to solve this problem?
Thanks for your help!

Is there any chance you damaged it doing your projects?

I don't think so. I didn't change anything and it stopped working when I wanted to upload a new sketch.

Press the reset button just before you choose upload. If your OS can see the bootloader the sketch will upload. The Leonardo needs to be programmed as a serial device to show as a serial port.