sounds like you may have a plugins issue. since you can’t get into your wp admin section go to your hosting file manager and rename your plugins folder to plugins_old and then try to get into your wp-admin section. if you can get in now then you’ve got a plugin that’s conflicting with something somewhere so you should delete all your plugins (after noting which ones you’ve got!) from the file manager on your hosting cpanel and then, re-rename the plugins folder back to what it should be and add them all in again one at a time until things go squiffy again and they you know you’ve found the problem.
also, check all your plugins at the repository to make sure they’re compatible with the version of wp you’re using. that could the problem and ultimately save you a lot of faffing about!
I read about that when I started searching, and it was the first thing I did, but it didn’t work. Thanks anyway!
make a test wordpress install in some folder of new version . In the and then replace its database with that of previous one . Be sure to change wp config . If that works then on your old site install a fresh version of wordpress files
