Access to full-text resources depends on your "affiliation," according to rules established by the university that apply to other privileges besides library access. You can check that affiliation by logging into OneCampus, search for the Manage Accounts category, and then click on Profile. Scroll to the bottom to see a list of your current affiliations. You'll need to see VT-ACTIVE-MEMBER listed under Affiliations to be able to have Off Campus Access to Library Resources.
New graduate students often don't get VT-ACTIVE-MEMBER until their assistantship starts (usually by the first day of classes), or they've paid tuition (could be after classes start). If you don't have that affiliation, contact the Graduate School to see what's going on.