Missing folder

Alright I’m going crazy. I’m trying so hard to understand why this isn’t working, but i can’t seem to fix it:

Whenever i try to upload an image of ANY filetype it stops and shows me this error: “IMG…..” has failed to upload due to an error
Missing a temporary folder.

I’ve also noticed that no images in any of the different themes i’ve tried will show up including headers, avatar, so on….). I’m using filezilla and one.com (mysql) as webhost. I’ve looked at several topics concerning the same issue, but whenever someone seems to have found a solution they explain it in a way that my non-tech-savy-head can understand… Can anyone please help me?

Michael