can not add links in new pages / posts

hi all.
so i have my existing site that has been active for a couple of years now.

on Friday i noticed when i went to add a new page / post the ability to add hyperlinks does not work.

When i highlight text / image to make it a link i click the button but no existing content loads and when i manually type an address in to link to and click okay nothing happens.

has anyone else experienced this? or know how to fix this.

cheers