I'm pretty sure it's a failure in the amp, but I'm gonna try with a new cable first. Otherwise I think it's time for me to get a new amp instead of fixing this old one. But thanks for the information!
My bass amp suddenly died, it's a Behringer Ultrabass BX 1200. No sound or light went on when I turned it on when I wanted to play :( Does anyone have any idea what's wrong? It can be something with the cables, but I'm not really sure...