Try the following basic troubleshooting steps:
Check your Internet connection. Hardwired connections work best.
Try logging out and logging back in again.
Try using a different browser. Chrome generally works well.
Try restarting your device.
Try clearing your cache and cookies.
If after trying all of the options mentioned you still have the same problem:
See this help article and this one for instructions on how to contact TurboTax customer support depending on which product you are using.