So I did not exactly follwed the instructions about the kernel and U-boot on the site. Now I have installed the U-boot with bootmenu for RX-51 and I did not want to mess it up so I created an uImage from kernel power49 but did not work and copied the uImage that my Ubuntu setup had created but did not work also. The U-boot finds the kernel and seems that everything is OK but after it says: "Starting kernel." nothing happens and the white led remains on but when a correct starup is made the led goes off automatically.