How to show hidden system and folders. Option disabled by a virus. (Windows XP)

If you enable "Show hidden files and folders" in the Windows Explorer, but still can't see any hidden files and folders and the corresponding checkbox in the folder properties is still unchecked, this is probably caused by a virus. To show hidden files and folders

Click Start -> Run -> type regedit -> hit Enter
In Regedit find

Code:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALL

Find the "CheckedValue" parameter and delete it.
Create a DWORD parameter and rename it to "CheckedValue". Set its value to 1.
Open any folder. Go to Tools -> Folder options -> View -> Check the "Show hidden files and folders" checkbox.