Compaq desktop and PPS files in Office 2007

Hi can anybody help me for some reason when I try to open pps files using my powerpoint(from Office 2007) it won't open it in the full screen slideshow view it will only open it in the small screen where you edit/make presentations and says compatability mode. Now this is where am confused as have same Office 2007 installed on Toshiba laptop and it changes PPS to PPT and opens it in the full screen slideshow but the desktop won't do this, it does the same thing opens in the small window where you can edit or make presentations, and wondering why, as can't understand why as am sure it used to although have to admit never look at file extension as powerpoint is set to open all these kinds of files. Weird thing is if I change PPS to open with Powerpoint Viewer 2003(which came installed on Compaq desktop) it shows it in the full screen slideshow.

Have tried, uninstalling powerpoint and reinstalling, repairing office, fixing broken file extensions and no joy still will only open PPS and PPT files in compatability mode in the small window, anybody got any ideas as to why one won't open them and one will using the same Office 2007 Home and Student disc?

Would greatly appreciate any help as can open them in slideshow but have to find the button in the edit window and so much easier if it will just open it straight into full screen mode. If I save the program in Powerpoint and then save as the new 2007 version of powerpoint then it opens it in the full screen mode fine but in PPS or PPT no joy small screen only Oh by the way I always save them to desktop then scan with Norton before opening them never open them straight from Windows Mail as know some can be fake and even if know sender still scan it just to be ultra safe.

Debbie(Simreaper)