MICROSOFT OFFICE has been installed, why not open PPT file

As usual, that there should be able to double-click to open it up, why has obviously downloaded MICROSOFT OFFICE 2003, but there are also those PPT WORD, PPT I still can not open the file?
Why ah ….

You look at the situation, please try to restart you computer! Ppt, and to ensure that your association office! Ah see is the 2007 and 2003 (97 2003) the two versions of the suffix is different.
Word
97 ~ 2003:*.doc
2007:*.docx

excel
97 ~ 2003:xls
2007:xlsx

slides (ppt)
97 ~ 3003:ppt
2007:pptx and no power pont related documents, in their own View the document in the file type association to see how ggg