Hello! I understand you're facing an issue where your screen dims after a few seconds, and you're unable to add content, regardless of the browser or computer you use. Let’s try to get to the bottom of this together.

1. Check Power Settings:
- Since your screen dims, it could be related to your power settings. Go to your Windows 10 settings by clicking on the Start menu and selecting "Settings" (the gear icon).
- Click on "System" and then "Power & sleep." Ensure that the "Screen" setting is set to a longer duration or "Never" while plugged in.

2. Browser Settings:
- If you haven’t already, try clearing your browser cache. Here’s how:
- For Chrome: Click on the three dots in the upper right corner, select "More tools," then "Clear browsing data." Check "Cached images and files" and click "Clear data."
- For Edge: Click the three dots, choose "Settings," go to "Privacy, search, and services," and under "Clear browsing data," click "Choose what to clear."

3. Disable Background Apps:
- Sometimes, apps running in the background may cause disruptions. Go back to the “Privacy” settings in Windows 10 (found in the main Settings window) and check the “Background apps” section. Disable any apps that you don't need running.

4. Browser Extensions:
- Certain extensions can interfere with web applications. Try disabling any extensions or add-ons in your browser and see if that resolves the issue.

5. Try Incognito/Private Mode:
- Open a new incognito (Chrome) or private (Edge) window in your browser and log into MyHeritage. This mode disables extensions and could help identify if they are the problem.

6. Check for Updates:
- Ensure your Windows 10 and browser versions are up to date. Sometimes, updates fix compatibility issues.

If the issue persists after these steps, it might require a more in-depth investigation. Please let me know how it goes, and we can proceed from there! Are you satisfied with the suggestions I provided?