Safari can no longer open certain sites.

Hello,

It is always good to have a second browser, if only to check if the problem comes from the browser or not.
Download FireFox: https://www.mozilla.org/fr/firefox/

Also:
It is important to indicate what your machine and your system are. Go to the Apple menu in the top left corner of the screen, then click on: "About This Mac".

Sometimes a simple restart is enough to sort things out. If not, follow the steps below, point by point, testing again before moving on to the next steps:

Updates:

1°) Go to the top left corner of the screen in the Apple menu, and select "Software Updates".

2°) Choose and download Onyx for your system http://www.titanium.free.fr/
Install Onyx.
Open Onyx
Let it check the SMART status of the hard drive and the volume structure, then give it the password when prompted
Then click the "Automation" button
Check all boxes except "Show folder contents"
Click "Run"
Restart the Mac.

(Use Onyx once a week for maintenance and problem prevention).

--
Best regards.
Pierre

So once again, after trying everything, no notable improvements... The same sites still don't work while on the other computers I have, they all work... these sites are Virtual Regatta and Tennis-Classim... Anyway, what should I do now? I’m still waiting for your help, thank you.

I don't really know what's going on, but I configured the system preferences on my Mac exactly the same way as another Mac at home... so I really don't understand why it's not working...
I don't know if I have the Ethernet cable, but I'll try to look for it to see...

If you are connected via Wi-Fi, try using the Ethernet cable.
Are the blocked pages still the same?

Otherwise, this combined update rewrites the system and fixes some errors: https://support.apple.com/kb/DL1399?locale=en_US&viewlocale=fr_FR

It also resolves some reliability issues, including with proxies: https://support.apple.com/kb/DL1429?locale=en_US&viewlocale=fr_FR

This fixes issues with certain applications: https://support.apple.com/kb/DL1512?locale=en_US&viewlocale=fr_FR

Try them one by one and retest before moving on to the next one.
It's unnecessary to remind you that you should always back up to another disk even under normal circumstances.
--
Best regards.
Pierre

Hi Pierre, first of all, thank you for your help, but I followed your advice to the letter and it's still not working :( Moreover, I had previously tried with Firefox but that yielded no results either. I'm a bit desperate, maybe it's my proxy and DNS settings that are incorrect? What should I put exactly in those cases then? For important information, I have a MacBook Air with version 10.6.8. Thanks for your help!

Well, here we go again, still the same problem. I had already checked the site forum.mac4eyer.com but the problem is not resolved...
It's surprising nonetheless, and otherwise, I don't know how to get it through the ethernet cable.
Any other ideas to suggest?
Thanks in advance.

it doesn't work better with ethernet...