This can be the result of malware and infection etc.
Removing adware & spyware
faq608-4650
This appears to be an "all or nothing" setting.
Registry Settings
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
Value Name: NoControlPanel
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disable restriction, 1 = enable restriction)
Display Applet.
Registry Settings
User Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
Value Name: NoDispCPL
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disabled, 1 = enabled)
"Show only specified control panel applets" policy does not display applets that use dynamic icons in Windows XP Service Pack 2
This article is a bit old and the names have been changed to protect the innocent but it might contribute something along the lines of replacing missing Applets.
Replacing Missing Control Panel Icons