Do you mean that you cannot delete the file name from the Most Recently Used file list? If so, then read this
Fill the MRU (Most Recently Used) list with bogus file names http://www.pptfaq.com/FAQ00373.htm
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Michael Koerner
MS MVP - PowerPoint
I can delete slides, but I cannot delete the presentation name out of power
point, what do I do?
if you want to delete your 'whole' presentation from your computers hard
disk....
Then
File > Open > navigate to your presentation filename > click the filename >
press the Del key on your keyboard > confirm that you want to delete the
file and move it to the recycle bin