My own laptop installed and finally ended on a similar black screen and mouse cursor.
In my case I hit ctnl+alt+delete, chose to log out and back in again, and the system was finally working. The issue in my case was possibly down with the laptops intel integrated gfx drivers not being compatible, not recognising the new operating system, as I was given an on screen intel pop up message after logging in again, stating if I changed resolution from what was default, I could damage the hardware. Resolutions that my system or monitor cannot handle, are currently not blocked out and are still showing in software that allows me to change the display, so if I choose a resolution too high, that could result in problems damaging the pc.
Compatibility is poor at the moment when it comes to some popular hardware. So far on various forums third party firewalls, old hp printer drivers and graphics cards of just about any era seem to be on top. Whether intel will bother to update my generic drivers for windows 10 compatible ones (on a two year old system) remains to be seen.
What are your specs? What operating system was installed before the update? Do you have integrated or (most likely) dedicated graphics? Googling 'black screen cursor asus windows 10' gives up similar issues but from what I can see no real solutions.
You might still be able to go back to last known config, or try a repair, or boot from a previous image eg
https://www.youtube.com/watch?v=-N28hQCmzY0
if anyone has a black screen (only) and dedicated gfx, it may be a case of non compatibility and or integrated gfx set back on. it might be solved by plugging in your displays hdmi or gfx cable into the integrated gfx port of your system instead of the dedicated gfx to get an image, then disabling the integrated display drivers within windows, setting dedicated gfx device drivers to automatic, then attempting an update after the next restart. for a laptop, try connecting to another device eg tv or monitor using a display cable that both are both capable of, such as rgb or hdmi