Broken featured image in Network

I dont know why the featured image in my website is not showing anymore, i mean it is displayed but is displayed as a broken image. I suspect it might be caused by the fact I tried to install the network multisite. I tried to get back and uninstall the network but i think i was unsuccessful. All the featured image that i inserted in the posts work fine, but if i delete it and set it again, it shows as a broken image. Do you have any idea why is behaving like that? I think it os because the root is changed, but I did all i was supposed to do to uninstall the MU.

I followed the procedure to uninstall the network:

.htaccess back to how it was originally
wp-config without the multisite allowed
I suspect it might have written something in my database but i checked: everything looks normal, there is nothing wrong or wiord table and such.

Please help, i m sure it is just a wrong path WP, but i apparentely i am not able to get back.