Unable to load after wp_login after new upload

I’m sorry I know there have been posts about this in the past, but they don’t seem to have been resolved or I can’t find an answer to my specific problem.
I’ve been modifying a Buddypress-enabled site locally using Xampp, which has the relevant phpmyadmin and mysql capability. I wanted to upload this site to a subdomain I have at lcf.locallysocially.co.uk. I have also installed wordpress afresh (new version) on the root of the domain as the aforementioned site is just a side project nothing to do with the site I’m due to make.
So I have uploaded my site to https://lcf.locallysocially.co.uk, changed the wp_config file to the correct name, login, pw, host etc (by the way i have already configured the root domain correctly and a sample theme I have is correctly installed so the settings in config should be right apart from database being different) and altered the address of the site (without the end slash/) to the intended site https://lcf.locallysocially.co.uk.
Now I can get to the /wp_login.php on the subdomain but then when it logs in, it brings up a blank page instead of loading up the dashboard, and my site says failed to load – internal server error HTTP 500 or just shows a blank page if I’m “logged in”.
Can anyone shed any light on why this is happening? Theories even?
I’ve tried to re-upload the site, I’ve imported the sql tables and cleared them and re-imported them to no avail and now I’m wondering if it’s because it’s on a subdomain? Any help welcomed. Thanks!

[No bumping, thank you.]