Raspberry 3 owncloud server crahses

Everytime i start the sync of my pc to my small owncloud server it fails... It tryes to sync files but quickly the whole server crashes.... Also putty and ftp will not work ones it's crashed. I can ping the device so i know it's connected to my router (wired) .
Does any one know how to fix this?
(Putty wil work realy realy slow)

My knowledge of linux is small so if i have to post any logs please tell me.

Perhaps you can still connect a monitor and keyboard to your RPi, then it could show an error on the screen. Your logfiles could contain some information, just check the files in /var/log/* around the time your system crashed. It's hard to say what to look for in particular as it could be many things.
You can also try to sync very few files and monitor your server, then you perhaps see which process is starting to consume all the resources (webserver, php, mysql, ...).