Make sure to open any SharePoint site using the Internet Explorer (IE) browser. Other browsers such as FireFox and Safari do not authenticate certain features that SharePoint allows.
Another reason for this could be that you logged in with a different account. All employees at Valencia College have two accounts. E.G. username@mail.valenciacollege.edu and username@valenciacollege.edu. Both of these accounts will work with SharePoint but, since they are separate accounts, each one has different permissions assigned to it. Make sure you are using the correct account if you don’t have access to the SharePoint website you are trying access.