Control Panel "System" icon doesn't work

[qwerty]

My "system" icon in explorer does nothing. I can see it, but clicking
on it does nothing, even as admin in safe mode. All other seem to
work normally.

I am running XP Pro with automatic updates, and Avira & Spybot.

My sysdm.dll file is located in c:\windows\system32 and "attached" to
the icon. A second copy is in \dllcache. Both are shown as
08/21/2008 08:00 AM 300,544

Running in a command window, from either directory, gives the same
results, as does safe mode. Either as a user or admin.

The icon worked several days ago, but I have loaded software, run
ccleaner and other software since then. I really don't want to
reload the system, and tried system restore going back a few days, no
joy.

XP came on the computer, but I have no disks, and don't know how to
extract a single file. Also, I really don't know enough to
intellegently wade through the registry without help, or how to
troubleshoot this further. So. . .

Please help.