After drive encryption computer boot shows only black screen with cursor, no login. Symantec Endpoint Encryption 11.1.2 HF2 was installed, and encryption reported successful completion. This happened on a Lenovo T470 only.
A single setting for Windows wifi connection caused the issue: Under wifi network configuration in Computer Configuration > Policies > Windows Settings > Security Settings > Wireless Networks under Advanced settings on the Security tab there is a section for Single Sign On. If the single sign on to "Perform immediately before User Logon" is enable, the machine will present a black screen with a mouse cursor instead of a logon prompt. Pressing CTRL-ALT-DEL at that point just flashes the blue background and then goes back to black, can't login.
Switching this setting to "Perform immediately after User Logon" brings up the login screen normally and login proceeds.