Problems after upgrading to WordPress 3.7.1

My website, http://technest.tk was running good and proper. Today I logged in to my dashboard and saw that there was an update to WordPress available. I clicked on ‘Update Now’ and tried to update WordPress from my dashboard/browser (I have done this several times before). This time, the messages just hanged on ‘Copying Files’, so after like half an hour I refreshed the page and went to the dashboard, which was not displayed and a message showed up saying ‘The site is under brief maintenance, please check back in a minute.’ I searched for the solution to this problem on the ww.wp.xz.cn support forums and saw one solution, which said ‘Delete the .maintenance file in your WordPress directory through FTP’, so I did it. Now when I visit my site, it says:
Fatal error: Call to undefined function wp_using_ext_object_cache() in /home/a9414691/public_html/wp-includes/query.php on line 2185
Please help me. I can log in to my websites dashboard, but can not go to useful pages like the update page, so I can update it again, but no, it just displays the error again.
What do I do? I am really worried! And no, I’m using free hosting, there is no backup over there or anything, just help me solve this by doing something through FTP or any other way.

Thank you.