So what you suggest for the back-up?
Normally a host backup should be fine, which is just a zipped copy of your files and a copy of your database. No idea how your host does their backups.
Or Should I try re-uploading the core Joomla libraries files??
I've already restored the library files. You can restore more if you want, but I suggest leaving it along for now as it's working.
(is your debug code still on my server and how can I use it in future, if its still there?)
No debug code needed. Was able to find the problem just examining file structure and files.
Thank you so much Kyle. Very professional of you for such prompt help in time.
Glad I could be of help.