See if you can't do a Crtl+Alt+F2 from the black screen to get a text login and then rollback the update via 'eopkg history' (to get # of system state before last update, then 'sudo eopkg history -t #'. If not, try tapping Esc or E upon first booting to see if you can get to the GRUB screen. At that point, see if you can pick a different kernel to boot, or maybe change up some boot options written below. If you provide some hardware details, I can make suggestions thereof. At worst, you'd have to chroot into your HDD via a liveUSB and edit some errant data. Solus is 99% recoverable via the above methods, and since the login screen flashed, you laptop graphics card probably hasn't burned out due to a catastrophic driver failure or power surge.