Go to your Safari menu bar. Click Safari > Preferences then select the Advanced tab.
Click: Change Settings
That will prompt the System Preferences > Network > Proxies pane.
If any of the boxes on the left are selected, deselect then click OK.
Quit and relaunch Safari to test.
If proxies aren't the issue, try troubleshooting Safari plugins and extensions.
From your Safari menu bar click Safari > Preferences then select the Security tab.
Deselect: Allow all other plug-ins. Quit and relaunch Safari to test.
If that made a difference, instructions for troubleshooting plugins here.
If it's not a plug-in issue, select the Extensions tab. If there are any extensions installed, turn that OFF, quit and relaunch Safari to test. If that made a difference, uninstall one at a time, quit and relaunch Safari until you find the culprit.