Hi,
No, you cannot change it in preferences. I suspect, the preferences are messed up internally. This is the reason, why I would recommend to try to trash them and build them from scratch.
To get to the Safe Start Mode, you have to first double-click the Cubase icon, and then immediately hold down “ + + ”, not the other way around.
If it doesn’t work, type %AppData% to the File Explorer. Then open Steinberg folder. There is Cubase 9.5_64 folder. Rename it to 2017_12_23_Cubase 9.5_64. Then start Cubase. You should get to the Cubase factory settings (you preferences is trashed).