Fresh install freezes when running glxgears

As the topic says, after a fresh install of LinuxCNC 2.9.2 the system crashes when I run glxgears...
The screen freezes completely and I can't input anything. It still works to move the mouse but I can't click anything. Keyboard shortcuts aren't working as well. 
What can I do?

My graphics card is a Nvidia 6600 GT and I did sudo apt update & upgrade after installing. 

Did you install drivers for graphic card?
Do not, they cause trouble with real time kernels.
Nvidia always caused issues with latency, but locking the screen, i never had that.
Does the motherboard have integrated graphic? If yes, yank Nvidia out and give it a try.

Hmmm might have installed some... How can I remove them? Or should I run a new fresh install? The weird thing is, that glxgears worked on that PC but now it doesn't anymore. I can't remember if I used the on board graphics or internal graphics card for that...
I'll hopefully look into it tomorrow and get back to this thread! 

okay so when taking out the graphics card running glxgears works perfectly fine. with the graphics card inserted it still doesn't work at all.

I also tried to use the option but that also didn't help. So is the only possibility to get this to work to just not use a graphics card? i thought when using one the latency of the pc will drop because the motherboard is not that busy or is that wrong?