@FrancesDurrant Please undo any compatibility settings you've applied for Sims 3. The game should run fine in Windows 10.
Your dxdiag lists a couple of Windows update errors, so for maintenance purposes, please run a couple of checks of your Windows system files:
- Hit Windows key-X
- Choose either “PowerShell (Administrator)” or “Command prompt (Administrator),” whichever option is offered
- Inside the window that appears, copy and paste “DISM.exe /Online /Cleanup-image /Restorehealth” without quotes into the window, and enter
- The system will start validating soon. If it throws an error, please list it here
- After it reaches 100%, hit Windows key-X again
- Again, choose “PowerShell (Administrator)” or “Command prompt (Administrator)”
- Inside the window, copy and paste “sfc /scannow” without quotes into the window, and enter
- Post the message you receive here
Restart your computer and run any pending updates: hit Windows key-i, select Update & Security, and click the button to check for updates. If any install, restart again when you're done.
Origin is also throwing errors, so it's a good idea to clean uninstall and reinstall it as well. This won't uninstall Sims 3.
- Quit Origin, then right-click on the Task Bar and open the Task Manager. Scroll through looking for Origin entries. If you find any, click on them and End Task.
- Clear Origin's cache.
- Download Revo Uninstaller (the free version is fine) from here.
- Launch Revo, select Origin from the list, and click Uninstall.
- When it finishes uninstalling, select "Moderate" under "scanning modes," and click Scan.
- If Revo finds any remaining registry entries, select all, delete, and click Next.
- Revo will display "Remaining Data and Folders." Select all of them except for the "Origin Games" folder, if it appears. (This is where Sims 3 and other Origin games are installed by default.) Delete the rest.
- Close Revo, and restart your computer.
Next, download the full Origin installer and run it. Here's the direct download link:
http://download.dm.origin.com/origin/live/OriginSetup.exe
Be sure to run both the installer and Origin itself as an admin: right-click on each and select "Run as Administrator."