Try this: (do every step exactly)
1. Click Start -> Run
2. Type regedit and click Ok.
3. Locate the key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ Advanced\Folder\Hidden\SHOWALL
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
7. Also change in NOHIDDEN change value to 1
8. In SHOWALL change value to 0
9. Re-check the folder options
10. Now change the values to the same
NOHIDDEN to 2
SHOWALL to 1
Strange, but works.