Here are some suggestions for troubleshooting your SharePoint site:

1. Check that the URL you are using is correct and that you have access permissions.
2. If this fails, try accessing the SharePoint site from a different computer or with a different browser.
3. Refresh the page or clear the browser cache and restart the browser.
4. Check that the browser you are using is supported by SharePoint.
5. Check the network connection and firewall settings.
6. Check if there is a proxy server and that settings are configured correctly.