Problem: You are not able to log into your Joomla backend all of a sudden . No login form is shown , you just see a blank white or blue screen .
Solution: I would ask my hosting provider if there were recent server upgrades or file restorations done recently that may have triggered this. If this is not an immediate post installation problem i would need to confirm this from the host.
Secondly you may check your Site/administrator/modules folder and see if the whole module folders are complete and especially the mod_login folder. If they are not, then download the files of the exact Joomla version you are using . Use FTP To reupload themissing modules back into the /administrator/modules folder.
Note. Take note that the target is site/administrator/modules folder and not site/modules folder
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