Sounds like a run of the system file checker could help there. That will repair and replace any damaged or missing system files along with correcting cross links to those from softwares on occasion. Type in "sfc /scannow" at the Run prompt with the installation disk in the cd drive. This tool requires verification as it goes along. And then what caused a problem here in the first place?
"Many trojan horses, viruses and other malwares make changes to the registry. They may one or more of the shellopencommand keys. By changing these keys they can make themselves be executed each time that you 'open' a certain type of file e.g. if they modified the exefileshellopencommand key then the trojan will be invoked every time you start any (!) executable file.
One common trick is to disable the registry editor, so that it is more difficult for you to get rid of the trojan horse. Yes, Microsoft provides such a key in the registry - under
HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System
you will find an entry DisableRegistryTools which can be 0 or 1. By default this entry does not even exist which means you are allowed to edit the registry.
Here is an installer script which you can download and have it execute and it should restore your original settings. It does not do any magic. It will simply reset the shell open command for executable files:
.exe, .com, .bat, .pif, .scr (screensavers!)
and also for .reg files (registry data files)."
http://www.delphifaq.com/faq/windows_user/f1013.shtml