Hi, 

I have a latitude E6440 running the latest Win 10. In the last few days, every time I start my laptop from sleep or off, a black block (see pic) appears on screen but otherwise the function of laptop is unaffected (I can click behind it etc). 

The block goes away after anything from a few seconds to a few minutes, not seemingly after any particular actions. Occasionally the block has gone grey or to flashing lines.

I updated to latest intel graphics driver but have seen no change.

Any thoughts very welcome.