cant update to 3.8

Hi all

everytime i start to do a update to 3.8 the page “/update-core.php?action=do-core-upgrade” gets a error. page cannot be displayed. Even when i click on themese page to change theme i get same thing

but on FTP i can see those files

then randomly i can see the themes page again after random clicking and refreshing.

After fiddling around the .maintenance file is stil there and website goes down till i dont delete the maintenance file. I have done all sorts to get update working but no luck

I managed to change theme to a default one. Tried update and same thing page cannot be displayed

Any ideas?