This sounds so much like my own introduction to Moodle...
First, when dealing with Moodle two things to remember, you can push hard on a door, but the door is most likely already open, and you can read and write, therefore you are well on the way to becoming a Moodle expert. If I can do it, then anyone can...
When committing to a backup or upgrade, do not try to back out of it - this is a surprisingly common error by anyone who does not understand a lot of programming. Always keep in mind that you are dealing with an application, Moodle, written in a scripting language, PHP. Cancelling usually causes more problems that it solves, complete the instruction and then fix it as you need to.
Before you do anything, go into the Appearance menu and then to Themes then select Theme, and make sure the theme has been selected, and then click on the "Clear theme cache" button. Refresh your screen. Likely is that nothing wioll happen. But do that first.
Moodle's database requires that the character set used is a Unicode UTF-8 InnoDB collation, and it has been since oohhh long time. If yours is not a UTF-8 collation then your host has provided you with a dodgey installation script like Fantastico, or something else, there are a few.
What you might be able to do is to keep your current database by going into the config.php file and in the bit that says:
$CFG->dbname = 'your\moodle\database';
and
$CFG->dataroot = '\\serverpath\\yourfolderpath\\yourmoodledata';
All you are doing is aiming your new Moodle at the existing database and moodledata folder, so hopefully that should work. (I have never actually done this, mainly because if anything goes wrong, I restore previous backups. I also keep a couple of test moodles, to try things before I fiddle with the production servers.)