Can't work with wordpress when I always get blanks pages

Hi there,

few days ago I installed new WordPress on my hosting server. I have a two sites:

1.https://strefapotencjalu.home.pl/wordpress-3.8/wordpress/ (fruitful theme)
2.https://strefapotencjalu.home.pl/danielkod/wordpress/ (balance theme)

BOTH on the same server. And exactly same problems, no matter what kind of browser or computer I use (Safari, Firefox, Mozilla, PC or MAC or whatever):

1. In ‘Pages’ section- I want to add new page, so I go to ‘add new’, enter the title and when I click text area… after one second it’s turn to blank page. And nothing happen. I have to go back and edit saved draft. After that it’s going alright, but it’s so annoying! ??

2. When media adding- I choose some files, then point ‘add media’, I can see loader and… ‘faild’. I close the window, go to ‘media’ section and there is ‘missing’ object. I can use it in post or whatever, but it’s so annoying! ??

3. Widgets- here I feel like Hulk when try to do something with that; I drag and drop some stuff, but when I put it down, page go blank. Always. Then I click ‘back’ and there is no installed widgets.

I think there is a problem with WordPress or maybe with my host. Like I said, I have two websites, different themes, directory, but the same version of WP.

Don’t know what to do.
Help ??