Hi Louise246890, I am Paulo and I'd like to help.
Have you checked using another browser if you'll be able to access those websites? If you can, then it may only be due to an outdated browser cache. Try to delete the site data and see if it works.
If you're using Edge, go to Settings > Cookies and site permissions > Manage and delete cookies and site data > See all cookies and site data. Search the website, click the bin icon to remove it, and check if the issue is fixed.
If that didn't work, might as well clear them all by pressing Ctrl + Shift + Del on any browser.
If you're unable to access them as well using another browser, it could be due to a Firewall or caused by an antivirus blocking your access to those sites. Do you use any of that? Did you check them?