I've tried uninstalling all the plugins that are not essential to the site, and I checked that the ones I need are compatible with my version of Wordpress (3.5.2). Unfortunately, the sidebars still aren't appearing.
Please turn on the debug mode in wordpress ( you can find instruction how to do it here: http://codex.wordpress.org/Debugging_in_WordPress ) and open widget panel. You should have some information ( errors ). Please copy it and paste here.
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Have you imporeted andy data to your wordpress?
Please send me a screenshot of this panel ( I mean Appearances >> Widgets).
With regards
You have got some widget conflict. Try to uninstall and deactivate them and check the Appearances >> Widgets page.
With regards
Firstly I recommend to disable plugins that were displayed on the list of widgets at last positions.
With regards
Please turn on the debug mode in wordpress ( you can find instruction how to do it here: http://codex.wordpress.org/Debugging_in_WordPress ) and open widget panel. You should have some information ( errors ). Please copy it and paste here.
With regards.
define('WP_DEBUG', true);
but no errors are showing up in the widget panel.
Please create a temporary login data and send it to through private msg on forum. I will try to resolve you problem from your wordpress.
With regards.
Thank you for all your help!