If you are using TurboTax Online, check your Internet connection. Logging out of TurboTax and back in, changing browsers (Chrome generally works well). There are some additional troubleshooting steps in this TurboTax help article.
Every computer has a unique combination of components, settings, programs, services, and users. This means TurboTax can install and run flawlessly on one computer, but another computer's configuration can cause conflicts when installing, launching, or running TurboTax.
If you have tried all of these steps, I recommend that you contact TurboTax Support for assistance.