Hidden files not shown

Symptoms: Hidden files not shown.
Repeatedly set at "Do not show hidden files or folder" though "Show hidden files and folders" is selected under My Computer>Tools>Folder Options...>View

Cause: Possible virus or spyware (eg systime.exe)

Solution:
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\Advanced\Folder\Hidden\SHOWALLd.
4) Look for 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.

Remark: The above method does not remove the virus/spyware stated. But you can try deleting C:\WINDOWS\System32\systime.exe (but it is usually hidden and can only be deleted at safe mode)