1. Check the Network and Sharing Center in Windows to check current network activity.
2. Restart the modem or router.
3. Reboot the computer and try again.
4. If possible, then switch off the firewall in order to rule out that it is not blocking certain websites.
5. Try using a different browser to access the site.
6. Run a virus and malware scan.
7. Call the local internet service provider to troubleshoot the issue.