(I see that Ken just posted a little before me. Follow Ken's advice if you understand his guidance.)
There are many ways that you can approach your problem(s), and I can give you a few ideas about what I would do. I see that Ken mentions nginx. I don't use nginx, I have a regular server.
1) Make sure to backup up your moodledata folder, your moodle database
, and your moodle application. I am not sure how big your moodle is, but try to move these to a safe place.
2) Attempt to install Moodle from scratch, into its own new folder. This may seem overwhelming, but it really should be straightforward. By installing moodle from scratch, you will learn whether or not your server
has all the pieces to run a real moodle, and you will get some experience. Follow the moodle docs
for installation. I give you the short version, using "2" as a way to keep your moodles separated.
a) Create a folder, one level down from public_html, called moodledata2. Change its permissions to 777.
b) Create a new database, called something like moodledb2. Add a user. Remember the user's password. Set the collation to utf8mb4_unicode_ci.
a fresh version of moodle, unzip it to a folder, such as ../public_html/moodle2.
d) In your browser, go to your moodle2 folder. Follow the installation steps of moodle.
I made a video showing how to do this for those who might have cPanel. I don't know if you do or do not. The video might be useful to watch.
If this works, then you can work on importing your old moodle database into the new. You can copy your old moodledata into the new. And you should make sure to match plugins between old and new.
If you have never done these kinds of things before, everything will probably seem very hard. Be prepared that some things won't work. You will think that we are all speaking some foreign language, like from the planet Mars. And it may be that your server is not equipped to handle moodle. I own a small VPS where I run my own small moodle.