Constant Crashes

Recently I got a new PC, wich ofcourse meant installing Minecraft again.
A few days ago I wanted to play with friends for the first time again but it wasn't possible.
When i entered a multiplayer server or created a new singleplayer world Minecraft would freeze and I would have to force stop it with the taskmanager.
If I managed to join a multiplayer server, it wouldn't any skins. Not mine, other players or NPC's.
Ofcourse after a few seconds it would also freeze again.
When force stopped, i.e. crashed, the console would put out the error code -805306369.
A google search made it out to be a RAM issue. But I tried dedicating 1, 2, 4 and 8GB of RAM and it didn't matter.
I hope you can help me, as I just would like to play with my friends.