Before you return it try these two simple troubleshooting steps.
Creating a temporary account to isolate user-specific problems: Isolating an issue by using another user account
Safe Mode or "Safe Boot" is a troubleshooting mode that bypasses all third party system extensions and loads only required system components. Read about it: Starting up in Safe Mode
Some things such as iTunes do not work in Safe Mode. It is not intended to fix anything. Restarting normally will restore your Mac's previous behavior.