From your Safari menu bar (top of your screen) click Safari > Preferences then select the Security tab.
Deselect: Enable plug ins
Quit and relaunch Safari. If that helped, then follow the instructions for troubleshooting plugins here.
And also try deleting the cache and cookies.
Back to the menu bar, click Safari > Reset Safari
Select: Clear History (also empies the cache)
Now go to Safari > Preferences again then select the Privacy tab.
Click: Remove All Website Data (deletes cookies)
Quit and relaunch Safari to test.