You can try these two solutions, not sure if it will work for you, the 2nd is for NT but might be the same on winx64.
Download TweakUI for 64bit then install it, there will be a tweakUI icon in the control pannel. Start it, then select Control Pannel, and then enable all the items that you want to see in the control pannel.
http://www.softpedia.com/get/Tweak/System-Tweak/TweakUI-64-Bit-Edition.shtml
2nd posible solution
Try just reregistering the icons first (rundll32.exe shell32.dll,Control_FillCache_RunDLL).
Replacing Missing Control Panel Icons
http://support.microsoft.com/?id=173132
Expand the *.cpl file from the Microsoft Windows NT 4.0 CD. The following example demonstrates how to expand the file Access.cpl from the Microsoft Windows NT 4.0 CD into the C:\Winnt\System32 directory:
expand d:\i386\access.cp_ c:\winnt\system32\access.cpl
For additional information about how to manually open the Control Panel folders, click the article number below to view the article in the Microsoft Knowledge Base:
180025 (
http://support.microsoft.com/kb/180025/EN-US/) How to Open Control Panel Folders from the Command Prompt
Type the following line at a command prompt to reregister the icons:
rundll32.exe shell32.dll,Control_FillCache_RunDLL
It kind of look (a part from the DX) like user icons and that the admin stuff is hidden. So you may have changed some settings, as you also talk about registry changes.
reg
http://www.kellys-korner-xp.com/xp_c.htm#cpiconsmissing
http://www.winguides.com/registry/display.php/522/
Group Policy
http://www.pcworld.com/howto/article/0,aid,97440,00.asp