Huge problem connecting to owncloud! please help

guys, i need you help! i upgraded my owncloud server from ubuntu 14.4 to 16.4 and now i can't connect to anything. what am i forgetting? i'm not that familiar with linux but i did have it running and it was working great. the OS is upgraded and working, i think all my files are still there but when i try the URL that i used to have, i get a 404 error. i'm thinking it might be a php error but i have NO idea on how to start or where to look. please help. i think i need to either start or configure php7, any help with that

This could have a lot of origins. Do you have access to the error log of Apache ? This is the first point to start from.
With the upgrade you might have upgraded the Apache server from 2.2 to 2.4. The naming of the config files for the virtual host changes in 2.4 as well as the syntax of the directives.
You migth also have a problem of permission.

Please also move this thread into the category as is not an issue of ownCloud itself but of your webservers configuration.