Blank Sign in on two PCs- fails with System Variable changed on Third

[Anonymous]

Hello. Three Dell Windows 10 newer PC(NVIDIA Quadro P4000, 8GB, 4 DP), all worked until last night/this morning. When I attempt to start AutoCad 2020,  either the blank dialog box with just Sign In appears, or just a white screen. I can see the user name- upper right corner, but when I click on it, I also get a blank box, with the autodesk- User profile at the top. When I attempt to open an existing DWG file, I get the error message " System Variable Changed" . When I view the change- it shows selection preview as the error, Prefered as 3, and current as zero, no where to change the current at this screen There is a option to reset all, but I am unfamiliar with Autodesk, so not sure what that will do.

I think it is a resolution issue with Windows 10 of some sort. Of the 4 PCs in the office, three are failing, the only one working is an all-in-one PC, with a different monitor setup then the Dells.  I would call, but I am not the owner on this account, and I am having difficulty finding the Autodesk help number.

Thank you for any help.

[ennujozlagam]

try setting the SYSMON variable to 1, if does not help follow the link, you can try to refer to this LINK and see if helps. thanks

[Anonymous]

Unfortunately, it crashes after a few seconds when I am unable to sign in, so I am not able to try any changes.

[vinodkl]

Try resetting AutoCAD to defaults. Here is how you can do that : How to reset AutoCAD to defaults 

[Anonymous]

These PCs only have the correct resolution when their monitors are turned on. If the monitors get turned off, Windows runs "headless", and lowers the resolution to below the basic for AutoCad. When the monitors are turned on again, the resolution resets, and autocad sign-in works again.

Thanks for you ideas.