Hi MagpieC,
Please forgive me, I'm not quite sure I understand what the problem is other than screenshots aren't where they are suppose to be.
If you're not able to find your screenshots what you maybe able to do is search for the word screenshots on your computer.
Click your Start button, and in the search bar, type in screenshots. Highlight (Mouse over) right click, and select Open to view the photos and to find out where the folder is located.
Depending on how many folders show up. You may need to do this a few times. Note where your files are.
You may need to do a little searching to find if your files are being saved to a different Electronic Arts folder. Since it sounds like you mentioned there is one on both the C: Drive and D: Drive.
C:/ Users > [username] > Documents > Electronic Arts > The Sims 3 > Screenshots
D:/ Users > [username] > My Documents > Electronic Arts > The Sims 3 > Screenshots
For me, all that's in my Sims 3 folder on my C: Drive is the empty screenshots folder. When I go look in my Sims 3 folder on my D: Drive, it has my saves, screenshots and other important Sims 3 files and folders. So this is where I would look for my Sims 3 files.
Something I like to do is make a shortcut to my Electronic Arts folder on my desktop. For easier access to game saves, screenshots etc.
Highlight the Electronic Arts folder (Mouse over) right click, and select Send to Desktop (create a shortcut). This creates a shortcut to your Electronic Arts folder where your Sims 3 files are saved.
I hope this helps, and Welcome to the forum!!
MrsFlynn