If I open a file from the task bar by double-clicking, I end up opening it twice because only a single-click is required. The result is that the second opening is "read-only". If I close that then the 1st open is okay except that my customized toolbars are destroyed.
Before you open the file check to see if the read-only attribute is turned on by right-clicking on the file and checking properties. If the file had been copied by copy/paste to a CD-Writer then the read-only attribute gets turned on. XCOPY turns off the read-only attribute so such files are not a problem, but most other utilities result in setting the Read-only bit.
Look at your windows Task Manager to see if you have more than one instance of Excel, see if Help is working.
From the shortcuts area of the Windows task bar only one click is needed. Double-click results in invoking twice.
Make sure the "Ignore other applications" is not selected under Tools, Options, General.
Something More to Check: File, Save As, Tools, General Options, Read-Only option is on the same dialog that you use to set a password
Clear out all files in the Temporary Internet Directory. Excel cannot have two files with the same name open at the same time.