This is what was temporarely disabling it. So I closed one at a time untill it was inabled. Or so i though So before restarting i opened all the same stuff again. Firefox Emperor (game) Outlook MSN Messanger and 2 chat windows Excell Game Maker Winamp My Computer Google Talk Adobe Photo Shop Calculator Notepad This is just an assumption, but i think if you hagve too many things open in your task bar, then it temporarly disables this feature. I had the following things running in my task bar. so i saved all my work and closed all my windows and it started working. None of my windows where displaying a thumbnail, just a bar with the title and if i hover my mouse over the show desktop part, nothing would happen. I did set it to 1 and back to 0 - no difference. I found a hint to a registry key, something in the line of 'desktopPreviewDisabled' and it is set to '0' (=enabled as all the checkboxes indicate). I switched between various themes but still no difference. I disabled one screen but this made no difference. What could be the reason for this? Desktop machine is a dual screen setup. In short: Desktop Preview (Peek) is 'Enabled' but not working and I cannot change the setting. Also, in the context menu on the 'Show Desktop' Button in the taskbar, the 'Preview Desktop' entry is checked but grayed out/readonly. And what's weird: The setting in the Taskbar properties is checked but grayed out/readonly. I hover the mouse over a window preview on the taskbar but do not get the 'show this window and make all others transparent'. What is not working is Peek :( That means: I hover the mouse over the 'Show Desktop' on the taskbar but get no transparent windows. I have choosen an aero theme and Aero is basically working (transparency, snapping etc.). Now I have it also installed on my Desktop - a much more powerfull PC (3GHz 4 core, Nvidia 8800GT). First I installed it on a notebook (C2D, Nvidia 9600GS) and got to see Aero and it's features. Hello, I have Ultimate Final from my MSDN subscription installed.

Aero themes greyed out