If QuickBooks Payroll won't update, it could be due to various reasons such as internet connectivity issues, outdated software, or incorrect login credentials. Ensure that your computer and QuickBooks software are up-to-date, and verify your login credentials. Check your internet connection and firewall settings to ensure they are not blocking QuickBooks updates. Additionally, try restarting your computer and updating QuickBooks Payroll again. If the issue persists, consider reaching out to QuickBooks customer support for further assistance at +1-855-948-3646.