Can't access Theme- or Plugin-Settings

Hello

I’m a beginner with no code-knowledge but I made a nice onlinestore with worked. After a while I couldn’t enter the Theme or Plugin-Settings, next to that I the woocommerce-dynamic-gallery didn’t work proper. So I started to deactivate all the plugins but still the same problem. After deactivating the theme (going to twentyfourteen) it seemed to work for a little while but now I got the same problem:

– can’t access the plugins-page
– can’t access the theme-page
– can’t upload pictures for the product

Now, next to that the site doesn’t work anymore. I’m sweet since hours and have no clue what to do. Is there anybody who could give me some dummy-advice?

Thanks a lot for your great support.

Sascha