Humor me and try this:
On your installation that has no plugins and is using the Twenty Twelve theme (like https://www.holidaysinluxor.co.uk/ for example) do the following.
– Make a backup copy of your wp-config.php file and put that somewhere safe.
– Copy that wp-config.php to wp-config-SAVE.php (I really like multiple safety nets).
– Open the wp-config.php file using the most basic text editor you have. Windows notepad is good for this and add this line above the “stop editing” line so it looks like this:
define('CONCATENATE_SCRIPTS', false);
/* That's all, stop editing! Happy blogging. */
Save that, clear your browser cache and cookies (do not skip this step, it will not work if you don’t clear that out on your browser), re-login and try again.
Is there an easy way of going back to the previous version.
It’s not recommended* but if you have a complete file and database backup prior to doing the 3.5 upgrade then you can roll back that to that earlier version of your install.
You’ll lose any new posts, pages, or comments since that backup and you should make a complete separate backup of your installation as a safety net.
Otherwise can someone recommend me a developer who won’t charge me a fortune
Aside from suggesting that you post to https://jobs.wordpress.net/ we really do not make or entertain those types of conversations here. Conversations like that get closed very quickly.
*Note: Some people have installed an earlier release on top of 3.5 but that’s not a safe thing to do.
