scimmiettarossa

I've tried again via Synaptic (with the same-name-package provided by repository), with no result,
 
Then, I've tried again via command line (as quoted below) with the .deb downloaded from your link, and this time  it worked!!
 
thanks a lot!!!
 
as you can see below, the packages name and versions are the same,but for some reason it didn't work, before:
xxx@xxx:~/Downloads$ sudo dpkg -i linux-u-boot-next-cubieboard_5.31_armhf.deb (Reading database ... 80549 files and directories currently installed.) Preparing to unpack linux-u-boot-next-cubieboard_5.31_armhf.deb ... Unpacking linux-u-boot-cubieboard-next (5.31) over (5.31) ... Setting up linux-u-boot-cubieboard-next (5.31) ... Updating u-boot on device /dev/mmcblk0 xxx@xxx:~/Downloads$  

This is the cause - on my CB1 was the same.
 
Just replace the boot loader and reboot is no longer a power off.