When i was upgrading ubuntu 19.04 to 19.10 while installing the upgrades, the screen went blank and its been 15 mins it is still blank .
Do you by any chance have an NVIDIA graphics card and have auto login enabled ? there is a bug reported here that seems to be affecting people https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1845801
I have seen some people report the same on the Ubuntu reddit as well.
There are some workarounds like in the link above or in this post Unable to login after upgrading to 19.10 from 19.04