Back-end access issues

[seventhstar]

I've been having some issues with my website. I'm unable to gain access to back-end of the Joomla site. I have searched online for issues relating to back-end access issues and have tried the following:
Ensured that the database table settings are correct and that the user has the correct password, changed the password, ensured that the user was enabled, ensured that appropriate plugins were enabled and accessible. I've also attempted to install a backup through an Akeeba backup using Kickstart. All didn't work.
I've attempted to access the back-end via Edge and Firefox and both browsers give the same results... nothing.
I've installed two add-ons on firefox to give me information on errors that might be appearing on the pages. Nothing appears on the back-end page, or the install page, but I do receive errors on the main front page. They are:
TypeError: jQuery.browser is undefined
 /templates/frankies2017/jquery.js:2:16929 k@()
 /templates/frankies2017/jquery.js:2:17721 fireWith@()
 /templates/frankies2017/jquery.js:2:12436 ready@()
 /templates/frankies2017/jquery.js:2:9841 D@()
 

Today I began the process of installing a clean install of the Joomla application onto the server and I can't get past the first screen of the install. I'll fill in everything and then click NEXT and the screen flashes and then does nothing.

Here is some information about my server:
Ubuntu 14.04
Just intalled JQuery 3.3.1 (Which I think is the culprit) - which was done for a different website - on the same server.
I'm currently running Joomla 3.8.10
The front-end appears to be working fine, except for login functions.

My server directory looks like this:
home/user/web/website/public_html and so forth.

I have SSH access (via putty) to my server and can modify scripts, however I do have multiple websites (most of which are all experiencing the same issues).

My programming knowledge is limited, however I'm very good at following step-by-step.

If you could help me with any of this, that would be great.
Here are a few links.
to the install page: http://glutenfreefrankies.com/site2/ins ... /index.php#
to the front-end which shows errors as explained above: http://glutenfreefrankies.com
to the back-end which doesn't show any errors, but also doesn't do anything: http://glutenfreefrankies.com/administrator