Main menu issue, main page shows for every menu item.

Hi,

Every version of UE I install has the same issue, being that for every menu item I click, the whole menufield is filled with the main window view, instead of menu items. Also at random moments the whole page turns black and text stuff starts to appear in the upper left corner. What can I do?
Can it be due to my screen? I use a 49" wide, but the window is scaled. Or my graphics card? Anything?
I’m all new in this, so sorry if my explanation is unclear.

Best,
Didier