I downloaded your copy of sysdm.cpl file and it opened to system properties with a double click.
Short of a reinstall of your os, I am running out of ideas. :)
were you able to open system properties in safe mode while logged on as administrator?
EDIT: can you right click on your sysdm.cpl and choose properties, then look at the security tab (has to be done in safe mode to view security tab) and ensure that your user name has full control of this file?
EDIT 2: as a last resort it may be a deeply embedded infection and I would suggest you try one of these sites where there are more knowledgeable persons to clean such an infection:
Malware removal sites courtesy of LemP
Or -- and I think this is what you really should do because your problem is likely to be buried pretty deeply -- seek guided malware
removal help from one of the specialty forums:
• Bleeping Computer: Am I infected? What do I do?
http://www.bleepingcomputer.com/forums/forum103.html
• MalwareBytes' Anti-Malware
http://forums.malwarebytes.org/index.php?showforum=41
• SpywareHammer: Malware Removal
http://spywarehammer.com/simplemachinesforum/index.php?board=10.0
• Spyware Warrior: Help with spyware removal
http://www.spywarewarrior.com/viewforum.php?f=5
• DSL Reports: Security Cleanup
http://www.dslreports.com/forum/cleanup
• Bluetack: Malware Removal
http://www.bluetack.co.uk/forums/index.php?showforum=172