Screen freezes everytime after I log in (NEED HELP)

I've been experiencing this for a while now. Whenever I log in on my pc on LoL, my screen freezes for about 30 seconds (more precisely: my cursor freezes). This happens after I enter the lobby page. Also, all the boxes in the lobby (advertisments/news/whatever you want to call it) stay black.

The same thing happens on my brother's laptop but not on my laptop (only my pc).

We play on the EUW server, but I don't think it's a server issue because it doesn't occur on my laptop.

I've cleaned cookies on my compter and scanned for viruses, but that didn't help.

Has anyone had the same issues or does anyone know how to fix it? Thanks in advance.

Edit: The boxes in the loby are no longer black, but the freeze after logging in still happens. So they seem to be unrelated I guess?

Edit 2: the black boxes are back.