Hi! I see you're having trouble opening the Killer Sudoku app puzzle on your Windows device using WebKit browser. Let's figure this out together.

To start, could you tell me:
- Are you trying to open Killer Sudoku through a browser or an installed app?
- When you say "can't open," do you see any error messages or does the app just not load?
- Have you tried restarting your browser or device already?

This info will help me guide you better with some effective steps. Meanwhile, here are some general troubleshooting tips for apps or web games not loading on Windows 10:

1. Clear your browser cache and cookies: Sometimes old files cause loading problems.
2. Restart your browser or try a different one (like Edge or Chrome) to see if it works there.
3. Ensure your browser is up to date.
4. Disable any browser extensions temporarily that might block content.
5. If you are using an installed app version: try uninstalling and reinstalling it to fix corrupted files.
6. Restart your computer to ensure no background issues affect loading.

If you've done these already, please let me know which ones, and we can explore more advanced solutions like checking network connectivity or potential app glitches.

Are you comfortable trying these steps?