SO, you have configured Win7 or Vista (32 or 64-bit) JUST the way you like it, except one small catch, you can't seem to right click inside the Start Menu?
Really simple fix, its just a setting change, and yes it CAN get turned on itself as I discovered.
A lot of suggestions said do a system restore, scan the hard-disk, but this is where you should go to first before deciding Windows has packed in and needs a reformat/repair.
Problem / Symptoms:
Unable to Right Click icons in the Start-Menu.
Unable to Drag/Drop icons in the Start-Menu.
Unable to perform all secondary actions associated with the previous two, such as pinning or deleting.
User/System changed settings on Start-Menu Properties.
How To Fix:
Right-Click the Start-Menu button or ORB if you have Aero Basic/Aero running, and select Properties.
Go to Customize... Button on the Start Menu tab, it should take you to this tab automatically.
Once open, scroll down about halfway, and re-enable Context Menus and Dragging and Dropping. IF it is already enabled but still not working, try disabling, apply, close this all out, and go all the way back in and re-enable it to confirm it changed.