Looks like some HTML is broken. maybe a missing closing DIV somewhere.

Did you flush all caches to make sure CSS is up-to-date

Otherwise probably it's from a custom plugin, try disabling (non-core) plugins until the problem goes away. Then you know which plugin caused it.

where can i disable the plugins? in the DB, the UI is kinda useless.

They worked in the 2.x branch.. but so much has changed in the 3.x branch. 

Its either Profile_Manager , Custom_Index or Elggbook_Pro.

Just need to get that sorted.

Have a look at http://learn.elgg.org/en/stable/appendix/faqs.html?highlight=disable#white-page-wsod

I haven't tested if this still works in Elgg 3

Or you can use the commandline to disable plugins

http://learn.elgg.org/en/3.0/intro/elgg-cli.html#available-commands

Well thanks for the link, i was able to isolate it to Elggbook_pro.

the CLI is amazing..

It looks like the method with creating the file mod/disabled still works on Elgg 3 to prevent the plugins from getting loaded. Though it looks like some cached views (like custom_index index page) still get served as long as the cache isn't flushed.