I cannot open any directory such as Home in Ubuntu. I found the answer here and tried it. I received errors as follows

In the terminal there is only one $ sign. No username is there. That was weird to me.
Also, I was not able to open browsers on Ubuntu 20.04. If I try to open Firefox I receive a popup message "Your Firefox profile cannot be loaded. It may be missing or inaccessible."
Lastly, the operating system freeze several times.
Can anyone let me know what's wrong with the operating system?
