after experimenting with a LCD on my Arduino UNO the Arduino board does not auto-reset when I plug in my USB cable.
"Auto-Reset" in the context of Arduino means the existing sketch restarts from the beginning. Is this how you are using "auto-reset"?
When I tried to connect the LCD for the first time the UNO turned off (power LED slowly fading out), when I disconnected the ground cable again the Arduino turned on again. Do you guys know what that means?
This means there was a short circuit somewhere.
There are two very bad practices mentioned here that you should avoid:
1. Do not disconnect Ground, disconnect Power. Ground is important.
2. Do not change connections while your circuit is powered. This will eventually lead to a mistake that will cause damage.