Let's work together so you can open QuickBooks Pro (QBDT) 2021 after the update, Dan.

There may be damage to your company file. You'll want to figure out if the issue is with QuickBooks or your data file.

QuickBooks might try to open your previous company. Please follow these steps:

1. Press and hold the Ctrl key, then double-click the QuickBooks Desktop icon.
2. Don't release the Ctrl key until you see the "No Company Open" window unless QuickBooks freezes or gives you an error.
3. Select a company file, then choose Open.

If you're getting the same results, do the Clean Install. This allows QuickBooks to add new install files when you reinstall. 

Also, make sure to check the system requirements for QBDT 2021. This is to ensure your computer is compatible with the newly updated program.

If you're still unable to open QuickBooks, I recommend contacting our Live Support Team. They can create a case to further investigate the issue.

Please leave a comment below if you have additional questions about opening QuickBooks. I'll be right here to help you.