The login is provided by Elgg core. I would first copy over the original files. If that does not work, I would disable all plugins: http://docs.elgg.org/wiki/Disable_plugin

Note: I moved this to Technical Support group

set permissions to 750. It is a lot easier than you may think. If you are using cPanel you can right click on the data folder and edit permissions. Turn off read, write, and execute for world. turn off write for group. That is just one way you can do the settings. You should do more research to find out what settings are right for you. If you are using linux and love bash commands you should use chown for this. 

or ideally move the data folder outside of the web-accessible directory

thanks a lot. it helps.