PS2 Keyboard with Arduino nano


I am using the Logilink ID0059 Numpad as a input device for the Arduino Nano via PS2. After trying a lot with the code I was suddenly able to get it to work. But after some while and a restart it doesnt work anymore. I already sent an email to Logilink if they know something about this.
Is there anything I need to consider when working with USB/PS2-Keyboards e.g. timings for the init routine?
To complete this post, I want to give an overview of my setup. A LCD is connected to analog pins 4 and 5, while a Temperature sensor DS18B20 is connected to the interrupt pin D3, the PS2 plug is connected to interrupt pin D2 (Clock) and pin D4 (Data).

Best regards