Ken, thanks for that info.  I didn't know you could do that.  I just now did it, but there is no change.  I did notice that the Fill Screen button works, but it is not all that useful since it fills the screen and chops off part of the photo so that you have to scroll to see all of it.  The Fit Screen button worked fine up until today.  PSE has not crashed or anything else.  Nothing strange has happened on my computer.  It just suddenly and mysteriously has stopped working.  Also, before I rarely even needed to use Fit Screen since a photo was normally opened as large as was possible while still showing the whole photo.  One other thing I have noticed (I don't know if this is new behavior or the same as before) is that if I use the Zoom Tool and click once it just barely enlarges the photo, but then if I click a second time it suddenly enlarges it quite a lot so that a bunch of the photo can't fit on the screen so you have to scroll.  I want the photo to be displayed just right like it was before. :-)

Additional info (maybe irrelevant).  I am using Win7 Home Premium 64-bit and I am always logged on using a user id.  When I did the Ctrl+Alt+Shift keys trick a UAC window popped up since I my user account does not have admin privileges.  Of course, I said okay.  I also let it rebuild the preferences.  PSE started and then I exited.  I restarted PSE again as a user, as I normally do.

photodrawken wrote:

 

Did you restart the computer after rebuilding the Preferences?

 

I'm also running Win7 x64 Home Premium under a standard user account (PSE10), and I don't get the UAC prompt.

 

I don't understand what you mean about the "Fill Screen button", but if you haven't updated the video drivers or made any other system changes, then there are a couple of other things to try:

1. Use a reputable anti-virus program to do a full system scan.
2. Create a new standard user account, and see if PSE works under that account.

I apologize for being late in returning and replying.  Yes, I restarted the computer after rebuilding the preferences.  At the top of my PSE 9 under the File, Edit, Image, etc. menus there is a section that has several things including buttons that say Fit Screen, Fill Screen, and Print Size.  I use MSE with the latest a/v definitions and did a full system scan.  No problems.

Coincidentally, today I saw a post from someone else on a different forum who is also using PSE 9.  He said a few days ago his suddenly starting doing much the same thing as mine.  Maybe Adobe has put code in PSE 9 to have it start acting up in 2012/2 so that we are encouraged to update to PSE 10. :-)