Screen flicker problem with T420s, from power-on -- before OS loads, even before boot.

Question

I've just bought a new T420s and installed Debian GNU/Linux on it.  Had no screen problems the first few days.
This morning when I turned it on, the screen was flickering -- like it was doing a very slow refresh rate or something.  Extremely noticeable, and quite annoying :-).  Interestingly, the flicker started from the moment the screen came alive, when I turned the power on.  It persists through the boot loader sequence and into the operating system, etc.  I have powered the machine off and back on several times since then, but the flicker is still here.
Now, there is one interesting fact:
The last thing I did, right before the flicker started, was use the laptop with a dock + external monitor.  Not dual monitor, just a single external monitor -- the laptop's lid was down when it was in the dock.  The external monitor worked fine; at one point I opened the laptop's lid just to see what the screen looked like (I was curious because the external monitor's dimensions were very different from the T420s screen dimensions).  The laptop screen had garbage on it -- a kind of distorted, miscolored, and mis-aligned version of my usual operating system desktop.  But that didn't bother me -- I was using the external monitor, and didn't need the laptop screen for anything.  I closed the lid and kept working.
That night I powered it down in the dock.  This morning I packed it up and took it to work.  The first time I powered up, this new flicker was there.
Does it have something to do with the fact that I used it with a dock and/or external monitor?  It seems suspicious that the problem started right after the first time I did that.
By the way, this is a T420s with the stock video card, not the fancier Nvidia card.
Any ideas how to fix this?

Answer 1

hey kfogel,
welcome to the forums.
could you remove your Nix and place back the original OS ? I would like to know if the flicker occurs when your unit is on Windows or if it occurs while it is on Debian.
if the flicker doesn't occur when you have windows installed; i would suggest heading over to http://support.lenovo.com and update your whole unit before attempting to use Debian.
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