I have a dell inspiron which I bought few months ago, it came with ubuntu 14.04, it was going well until I upgraded to 17.10, when I power on the system it boots up ask me to enter decrypt password I enter it, it shows me the ubuntu logo and then black screen, it does not put me into the login screen, then I manually power off the system with power button, I repeat these steps until I get the login screen, I get login screen after 4-5 reboots.
I installed a boot repair tool and logged my system info in the following link,
ctrl+alt+f2
it will get you to tty2; login and debug; instead of rebooting maybe just restart display manager; seeps aux | grep -i dm
might be gdm..