Use the Task Manager (Processes tab) to see if iexplore.exe is running. Kill it from Task Manager if it is running.
Also make sure that any kind of messenger applications must be closed before you can install Flash Player.
P.S. do not kill explorer.exe - that is a system process that should always be running.
I am having the same issue. I closed iexplore.exe and still no luck!
Did you also close all messenger applications (Windows Messenger, MSN Messenger, Yahoo Messenger, Skype, etc., etc.)?
[topic moved to Flash Player forum]