flickering screen ...

My monitor has been annoying me lately. It's flickering occasionally. Sometimes a lot, other times not at all. It's irritating as hell anyway.
Strangely, it's just the primary screen, the secondary one (same make / model) doesn't flicker at all.
I've tried different power cables and a different power socket, switching cables, disconnecting cables and the graphics card, etc.

Don't really know what it is. So I'm downloading the latest drivers - and the nvidia website somehow manages to serve XP drivers even when selecting Vista as an OS ... Of course I only noticed after the download had finished and I tried installing it ... Very strange indeed ...