I just fixed the same thing following the steps written here:
Go to registry editor by running regedit in the run box.
Go to this key:
In the right hand area, double click hidden and change the value to 1.
Now you're all set to go. Check it in your tools menu if the changes have taken effect.
Method 2: (By Random Hajile)
1. Click "Start" -> "Run..." (or press Windows key + R)
2. Type "regedit" and click "Ok".
3. Find the key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer
4. Look at the "CheckedValue" key... This should be a DWORD key. If it isn't, delete the key.
5. Create a new key called "CheckedValue" as a DWORD (hexadecimal) with a value of 1.
6. The "Show hidden files & folders" check box should now work normally.
hope it is useful to you as well.