Question : Some Excel 2007 worksheets open with blue screen (previous thread no help)

I have been using Office 2007 and Excel for many months now.
Just today some of my Excel worksheets open with the blue screen, and can be viewed only using the View/Full Screen mode.  This has happened both to a new worksheet and to others I have been able to open normally until today.
I am not aware of any recent change in software that might explain this.  A previous thread in EE mentions the file pdfmaker.xla; there is no copy of this on my computer.  (I have checked with Windows search, set to view all files, and with X1 search.)  
A fix of unchecking "Ignore other applications that use ... DDE" in Excel options has not worked (it was not checked; I tried checking then un-checking, it seemed to work for one instance and then the problem returned.)
Other suggestions found elsewhere included opening files or Excel while holding down Ctrl; this did not cure the problem for me.
Any suggestions please?

Answer : Some Excel 2007 worksheets open with blue screen (previous thread no help)

Do you have multiple monitors, or have your workbooks been opened on computers with multiple monitors? (I am assuming that trying to Unhide the workbooks does not work?)