Edit >> Preferences >> Performance
Lightroom >> Preferences >> Performance (on Mac OSX)
Then disable GPU acceleration.
For Windows you should go to the website of the manufacturer of your graphics processor and check for driver updates. After updating you could try switching GPU acceleration on again, otherwise leave it disabled.
On mac GPU updates happen with OS updates.
Thanks that did get rid of the blue screen with the white cross. That's great.
I still cannot get the thirds guideline on my photo and when cropping and trying to straighten it wont bring up all the gridlines.
So appreciate you getting rid of my blue screen though, thanks so much
You can usually cycle through the different overlays by tabbing with the O key.
OMG how simple was that!! I have been looking and looking. When I went to tool overlay I couldn't tick anything but obviously didn't have the crop tool ticked. It was becoming frustrating. Glad it wasn't anything too complicated.
Thanks so much Joe