Symptom

When you try to launch an application (.exe files), the program does not run and a message is displayed that Windows cannot open this file. Windows doesnot know what program created the file.

Cause

This problem occurs if the .exe file association in the registry is corrupt. This behavior is generally caused by viruses; one of which is SirCam virus, which modifies the .exe file association in registry.

Resolution

Click Start, Run and type Command. If even this doesnot work, choose "Select the program from a list". In the selection window browse to "C:\Windows\System32" and select "cmd.exe"

• Type the following commands one by one:

cd\windows
regedit

• If Registry Editor opens successfully, then navigate to the following key:

HKEY_CLASSES_ROOT \ exefile \ shell \ open \ command

• Double-click the (Default) value in the right pane
• Delete the current value data, and then type:

"%1" %*
(ie., quote-percent-one-quote-space-percent-asterisk.)

• Any other entry can be deleted.
• Navigate to:

HKEY_CLASSES_ROOT\.exe

• In the right-pane, set (default) to exefile
• Exit the Registry Editor.

For reference what the contects of the registry keys should be, you can download them here.