If I get your report right, once you performed the reset you were able to access the router again (this should happen with "admin" and the password on the sticker) and then you attempted again the update to latest.
If this is the case, reset again BUT DO NOT attempt updating to latest.
Once (if) you have access, do not change anything, and perform an upgrade (or possibly a downgrade) to an older (but surely working) release, as holvoeth suggested 7.19.4 is a good candidate.
You don't specify this, but likely you attempted accessing the device via Webfig (the interface accessible from a browser).
In this particular release (7.20.4) the Webfig has been reported to be flaky, so use instead (if you run Windows) the dedicated Mikrotik tool, Winbox 3.x (if you are running Linux or MacOS, you can use Winbox 4.x, which - while still not fully finalized - is anyway much better than Webfig) read this:
How to downgrade:
-
download the relevant file, from here:
https://mikrotik.com/download/archive
should be:
https://download.mikrotik.com/routeros/7.19.4/routeros-7.19.4-arm.npk -
access the router in Winbox open system packages and drag and drop the file to it, this video - even if related to an older version - is still valid:
https://www.youtube.com/watch?v=SPZZZfYzGOI -
perform the downgrade either pressing the downgrade button or opening a terminal and running in it /system package downgrade