Thanks Ataraxy,

My display adapter is ATI Technologies ATI Radeon HD 4600 Series, there was an update available (Version 8.791.0.0 26/10/2010) which I have installed.
I have two Samsung SyncMaster monitors which were using the Generic Microsoft Drivers which I have also upgraded to Samsung.

My problem is intermittent, I haven't picked what brings it on yet; right now everything is OK so I guess I wait and see if these updates make any difference.

Thanks again . . . I'm learning.