Having trouble accessing certain websites across all browsers can be a frustrating experience. Here are several methods to diagnose and fix the issue:

1. Check Your Internet Connection:

Ensure that your device is connected to the internet. Try accessing other sites or use another device to verify the connection is working correctly.

2. Restart Your Router:

Sometimes, simply restarting your router can resolve connectivity issues.

3. Clear Browser Cache and Cookies:

Over time, your browser collects data that may cause conflicts. Clearing cache and cookies can often resolve these problems.

4. Disable Proxy Settings:

If you’re using a proxy, it might be restricting access to certain websites. Check your proxy settings and disable if necessary.

5. Flush DNS Cache:

Outdated DNS records can prevent access to websites. Open command prompt or terminal and type `ipconfig /flushdns` on Windows or `sudo killall -HUP mDNSResponder` on MacOS to flush the DNS cache.

6. Use Different DNS Servers:

If the problem persists, you might want to try using public DNS servers like Google’s (8.8.8.8 and 8.8.4.4) or Cloudflare’s (1.1.1.1).

7. Disable Network Adapters:

Sometimes, disabling and re-enabling your network adapters from the Control Panel can fix connectivity issues.

8. Check for Malware:

Malware can interfere with network connections. Run a comprehensive security scan to look for any malicious software.

9. Disable Firewalls or Antivirus temporarily:

Firewalls and antivirus programs can block access to certain sites due to perceived threats which could be false positives.

10. Reset Network Settings:

As a last resort, resetting your device’s network settings might help resolve connectivity problems.

If none of these steps help, it might be an issue with the website itself or with your internet service provider (ISP), at which point contacting support may be necessary.

Remember, it’s important not to compromise security while trying to fix access issues; always ensure that any changes you make are safe and reversible if needed.