I purchased new macbook air and new 2016 version of MS office was installed. I copied files from my PC external hard drive into the macintosh HD. All ms word and ppt files could be opened. I started working on an old ppt document for past few days. Suddenly from today, the ppt file is saving into my desktop but not into the macintosh HD. Then I opened a new pptx file and tried saving it and it is same result. MS word files are fine. Why are my power point files not saving into my macintosh HD.