Game won't start

Hello.

I have BF4 on Steam (PC), played a bit over 200 hours by now.
However, since yesterday I have a problem that makes it impossible to play the game, I will explain.
At first I was able to enter game and browse servers, I see there are people in these servers (obviously since otherwise I assume these forums would be filled with complaints) but I can't join any of them! Trying the matchmaking option also didn't work.

I would only receive this message:

"FAILED TO JOIN GAME SESSION
An unknown error occurred. Error code: 1"

I tried restarting the game and then restarting my computer but it didn't help. :/

I figured I would try the next day, however, today the problem even escalated. Now I can't even start the game!
The EA launcher app opens, and it tells me "Preparing game..." but then NOTHING happens, sometimes it even gets stuck in a long loop where the "Preparing game..." disappears, but then starts over and then disappears and reappears again before finally just it ends and nothing happens.
I tried several times, both to run the game and to restart my PC, yet the problem persists, running the game as administrator changes nothing.
I saw 5 other persons report this same problem on Steam's community forum for BF4, but I found no solutions online (my other Steam games work fine).
I have no idea what could cause this...

Please help. <3