I recently installed (updated) Quicken 2020, Version 25.21, US version, and it fails.

JaymeHume9

When I try to open it, I see my files for a split second, then a blank screen, then a login screen for a split second, then the blank screen again. I contacted Quicken support, and for two hours we got no where. I contacted Best Buy's Geek Squad, and they reviewed all my settings, permissions, updates, but again got no where after two hours. I'd like to go back to my old version so that I could pay my bills, but I'm concerned that if I do, data may be lost due to the update.

Sherlock

I suggest you attempt to open the application without loading the data file: press the Ctrl key while you attempt to open Quicken.  If the application opens, I suggest you access a recent data file backup.  Otherwise, I suggest you perform a clean uninstall, install and update.  If you haven’t already, you may want to review: https://www.quicken.com/support/using-qcleanui-uninstall-quicken