In order to change the way that folders are displayed, you need the correct permissions. Make sure you have Administrator privileges on your computer and try again. Another problem that sometimes comes up is a viral one. The easiest way to fix this is to just run your own anti-virus checks and repairs, then try again. If it still doesn't work, then you'll have to fix it yourself.
From the Start menu, select Run and type "regedit" into the window that appears. You will then get a window with a file tree on the left. Expand the tree in the following order:
- HKEY_CURRENT_USER
- Software
- Microsoft
- Windows
- Current Version
- Explorer
- Advanced
From there, simply double-click Hidden on the right, and set the value to 1. This will allow you to once again change the Folder Options and reveal those hidden files.