Display doesn't work without Inputkeys

Hey there, i have a question: I used ther library a lot of times without any problems. No, i am building up a new board with a 20x4 lcd. first, i connected the lcd to the Arduino Uno, but i didn't connect any keys for input. Later, i wanna use normal keys with pullup_input, i did this before without any problems.
But after wiring the lcd, i would make a test for the wiring. I compiled my menu and uploaded it to the Arduino. The display doesn't work, there were no lettes on the display, only symbols.....
Then, i selected "No input required", and everything was working fine. Why that ?????
When i will connect the keys, and no key is pressed, it will be the same hardware!!!!

What happend here ?

Hi there, it's difficult to say what happened without diagnostics or debugging, but the most likely case is that one of the pins was somehow floating and causing switches to constantly fire, in this case switches cannot handle that particularly well. Or even a pin that was used by a shield or something like that. Any pin that successfully configured as pull-up should not cause problems, as it is essentially in the off state.

If you have a scope to hand, you could take a look at each of the pins and see if one of the pins was floating / changing value.