symptom
My Ubuntu 20.04 gets freezing right after I log in (after a few seconds). I can only move my mouse cursor;I cannot select and click anything with my mouse and the keyboard doesn't work too. If I log in with another user (i.e. administrator) I don't have that problem.
It seems that there are some same issues (e.g. Ubuntu 18.04 freezing after login, only mouse movement working) but answers there don't work for me. Also, I am not using Nvidia; I am using an internal one of intel.
history
This problem happened when I was using the Libre office. Whenever I save a document or change the keyboard language (i.e. English to German), it froze. I forcefully rebooted the machine with the power button about 5 times whenever my machine froze. After that, I got the Busybox problem (i.e. boot not to the normal Ubuntu, but to a kind of command line). I solved this problem by resetting the boot option according to this site (https://askubuntu.com/a/1157394). But, it still keeps freezing.