I was having trouble with a CX nspire. The startup sequence would run and then the calculator would go into a dark grey screen that seemed to have moving lines. I reset several times, no success.
What fixed it was the following. I switched out a battery from a good calculator. With the good battery, the computer was able to restart and run normally. When I put the old battery back in, the calculator also ran normally. (while connected to power on the usb cable)
I am going to let in charge for a while and see if the fix is permanent. I may have to buy a new battery but at least it is working now.