PS/2 Trackball problem

Hi all! I'm having some problems with this Trackball from Sparkfun and I can't find anything about it, so I thought maybe someone here can help me. I tried asking in the spanish forum but nobody answered so... Here's the situation:

I'm making a MIDI panel for Davinci Resolve and I need 3 trackballs. The first I bought just arrived and I can't communicate between the trackball and the arduino.

I cut the PS/2 cable and I soldered the 4 cables to different cables with dupont connectors, to use on the breadboard. I looked around and i suppose this trackball works as a PS/2 mouse, with 1 5V, 1 Gnd, 1 CLK and 1 DTA.

Here's an image gallery.

I'm using this code and this library, which is the only thing I found online, but i can't get it to work. When I upload the code, the Arduino doesn't show anything on the serial monitor. I tried changing the CLK and DTA cables but i don't seem to get any signal. The 2 'On' LED's work fine on the trackball, so I assume it's working.

I'm still learning so I don't really know how to approach this. How could I debug this and find the error? Thanks for your patience!