X won't start
I've had a string of problems with this card (XFX GTX 260 black) always, but they have been tolerable. My second display often gets completely corrupted (screenwide flicker of whitish color, goes away by rebooting) while playing or watching HD video on primary display, or the whole computer might completely freeze when doing something with the GPU (CUDA, HD video or 3D games, never with plain desktop). Sometimes it has frozen so badly that a simple reset won't help, instead I've needed to take the power off for a few seconds to get to GDM again. All this while temperatures are nothing critical, nor anything else obvious going amiss.
But now starting X in boot does not work anymore. Instead the X just fully uses one complete core for kernel code (according to htop). I can't even generate the bug report, as the nvidia-bug-report.sh freezes too.
Any hints on how to start debugging this last problem are greatly appreciated, solving the original problems are a bonus.