It seems your Joomla! instance is corrupted. Since using the Joomla admin does not help with the re-installation, I would suggest Do a complete Joomla! Core manual re-installation / package replacement.
Note: This probably will work better in a local clone of the website on your desktop. Generally avoid doing this on the live website directly.
Create a fresh the Joomla! Core on an existing website:
Download your Joomla! version (3.7.3) full stable package from joomla.org
Start replacing everything Joomla! core in your instance.
Open side by side the 2 folders where your site-clone and the unzipped fresh Joomla package reside.
Navigate in each of the admin site subfolders:
a. Components, Modules, Includes folders.
Select all and copy the *subfolders/subcontent from fresh Joomla! of the above folders, and paste to your site. Let it replace any existing items.
*subfolders = each core component, module folder and files -see screenshot
b. Help, Manifests, Languages Folder
- Likely you won't need to replace anything for these folders- but in case you do, select the content of their subfolders, copy and paste to your site's instance. (e.g. for languages, copy the contents of the core en-EN language folder and paste them to your site - replace existing ones).
- Unless you have any template overrides you can copy/paste the whole templates folder. If you have overrides, then save your overrides somewhere before replacing the templates and place them again to their previous location on the fresh templates.
Navigate in each of the site subfolders:
a. bin, cli
- Select all and copy the files of these folders from fresh Joomla! of the above folders, and paste to your site's instance. Let it replace any existing items.
b. Includes, Layouts
- Copy the whole folders and replace on your site's instance.
c. Components, Libraries, Media, Modules
- Copy the subfolders/contents of these folders (the ones of each module, component etc - as described for the administrator components) and replace on your site's instance.
d. Languages and Templates
- Navigate in each plugin's folder and copy the subfolders that exist there. Replace the items with the same name on your joomla site instance.
- Similar as described for the admin site. Just note that if you are using 3rd party templates - then you need to copy from the fresh core only each subfolder that exist in the templates folder and not the whole folder.
Conclusion - things to keep in mind:
- The above describe briefly how to completely replace the core Joomla files on an existing Joomla site - without removing 3rd party files.
- With this general approach, it's made sure that the whole Joomla core is there.
- Of course it's recommended that the Joomla versions should match.
- Other specific customizations/overrides/patches over the core of the existing site will be removed.
- If there are no 3rd party extensions and other files exist on the whole website or partially in subfolders e.g. a plugins folder, then the whole parent folder can be replaced.
- Always have a backup - avoid doing such tasks on the live website.
- Remember to clearing caches etc, when testing your changes.
- I am describing/suggesting the full core re-installation with this method because likely if there is a failed Joomla installation for whatever reason, this might contain more than 1 corrupted files. However, someone could go with partial replacements of the whole Joomla package and try on each step to see if a specific issue is resolved.
I have found that in some cases, during copy/paste/replace from fresh Joomla to the site, it's useful and timesaver to temporary rename and keep aside some of the existing site folders - instead of replacing them (which deletes them) - so to keep references to them in my current working environment - without the need to look to re-download/re-unzip/recreate the existing site. I can easily rename folders and switch between the 2 versions - or do comparisons etc.