Looks like the file association is messed up. I suggest this after viewing the screen shot in your initial post.
Your screen shot shows the file type is a PowerPoint 2007 (or 2010) file but the "Opens with" program is incorrect. Click on the "Change" button in the Properties window - if PowerPoint is listed in the "Recommended Programs" select it (click on it) then click the OK button.
If PP is not listed, click the "Other Programs" drop list arrow (on the far right) - if PP is listed, click on it then click the OK button.
If PP isn't listed in "Other Programs" click the Browse... button and navigate to your Office installation. Select the PP executable POWERPNT, click the Open button, click the OK button, click the Apply button, click the OK button.
Clicking a .pptx file should now open in PowerPoint. Good luck.