Why is Aero Snap not working and how do I turn it on?
I discovered a much easier way on enabling / disabling the snap function:
Go to Control Panel > Ease of Access Centre
Select ' Make the mouse easier to use' ( I know its nothing to do with the mouse) At the bottom under 'Make it easier to use windows' mine had a checkbox with a tick in under 'Prevent Windows from being automatically arranged when moved to the edge of the screen'
It now works again, I'd never seen this page before but yet the checkbox was checked, I can only put it down to a corrupt file
Click "Windows key + U". look under "Making the mouse easier to use". Like it has already been stated, make sure that it is not checked; however, I found that mine was not checked, but understanding how windows can be I "checked and applied it then disabled it". This fixed it, go figure :)