Thanks - I read that before. The flickering /snow happens with Netfix site too - just logging into the Netflix site does it. Strangely its just the screen - if I switch the screen off and on it usually corrects itself. Very weird.
There are reports of similar problems with Netflix. Seems to be down to the Silverlight plug-in,
in some cases an update or re-install solved the problem.
Some mention too little Ram in their laptops/ PCs.