If you find that the Aero Peek feature is not working in your Windows 7 even after you have enabled it through the Control Panel, or through the Taskbar & Start Menu Properties box, it is quite possible that you may have tweaked your visual settings, as a result of which your Aero Peek too may have got inadvertently disabled.

Aero Peek not working
Perhaps this may help you:
Open Control Panel > Performance Information and Tools > Adjust Visual Effects.
Ensure that the Enable Aero Peek box is checked.
Also ensure that:
- Enable desktop composition &
- Use visual styles on windows and buttons
is checked. Clicked Apply > OK.
Better still, select Let Windows choose what’s best for my computer and click Apply/OK.
It should help!
But iff it doesn’t help maybe your Desktop Manager Session Manager Service has been disabled and the Desktop Window Manager too disabled.
In such a case you may want to see this post on How to troubleshoot & Fix Aero issues in Windows 7.
If you have liked this post, you might want to check out some more, on topics like Aero Peek, Tips.