Warning: Take your time reading this first sentence:

Before typing the following keystroke, remember that Ctrl+Alt+F7 is your friend. This is the keystroke to type to get back to where you are right now. (probably your guest session) OK? Remember? Sure?

OK! Now press Ctrl+Alt+F1 to go to TTY1, which is a full screen terminal (and only a terminal: no mouse, no dash, no nothing). Try to log in there.

It does show your user name when you type it after the login: prompt, but does not show anything when you type your password! Oh, and you have to type Enter after you typed your user name and before it shows you the password prompt.

Now type the following commands: (assuming user is your old user name)

sudo adduser user2

and follow the instructions on-screen. If you're not on a US keyboard, don't use any "special" characters like £ à ŷ ü nor any numbers unless they're from your keypad.

Now type the following commands:

sudo adduser user2 adm 
sudo adduser user2 cdrom
sudo adduser user2 sudo
sudo adduser user2 dip
sudo adduser user2 plugdev
sudo adduser user2 lpadmin
sudo adduser user2 sambashare

(If any of the above gives an error like group not found, don't worry: I'm trying to be thorough)

Now, log out of the guest session and log in as "user2" and come back here to this site

Ah you're back! ;-) Please test now if you still have your problem... No? OK!

Now,

1. Open the file manager
2. Browse to the /home/user directory
3. Copy (don't move!) all the files from Downloads to /home/user2/Downloads
4. Check you did a good job.
5. Now delete /home/user/Downloads
6. Go back to step 3 and repeat for Documents, Videos, ...
7. In a terminal type the following command: deluser user --remove-home

Done!